• 소음진동
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• 제5권2호
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• pp.247-256
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• 1995

In this paper, double exposure holographic interferometry using ruby pulse laser is formed in order to investigate the propagation of transient waves. The vibration characteristics according to the change of impact load direction, i.e., impacted in the shear direction and in the normal direction are analyzed. It was observed that the macroscopic trends of transient wave generation and propagation in the assembly of precipitator plates were almost similar regardless of the change of impact load direction. But the propagation and mixing of transient wave was advanced relatively slowly when impacted in the normal direction.

• Structural Engineering and Mechanics
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• 제30권3호
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• pp.369-382
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• 2008

An oscillator of two lumped masses linked through a vertical spring moves forward in the horizontal direction, initially at a certain height, over a horizontal Euler beam and descends on it due to its own weight. Vibration of the beam and the oscillator is excited at the onset of the ensuing impact. The impact produced by the descending oscillator is assumed to be either perfectly elastic or perfectly plastic. If the impact is perfectly elastic, the oscillator bounces off and hits the beam a number of times as it moves forward in the longitudinal direction of the beam, exchanging its dynamics with that of the beam. If the impact is perfectly plastic, the oscillator (initially) sticks to the beam after its first impact and then may separate and reattach to the beam as it moves along the beam. Further events of separation and reattachment may follow. This interesting and seemingly simple dynamic problem actually displays rather complicated dynamic behaviour and has never been studied in the past. It is found through simulated numerical examples that multiple events of separation and impact can take place for both perfectly elastic impact and perfectly plastic impact (though more of these in the case of perfectly elastic impact) and the dynamic response of the oscillator and the beam looks noisy when there is an event of impact because impact excites higher-frequency components. For the perfectly plastic impact, the oscillator can experience multiple events of consecutive separation from the beam and subsequent reattachment to it.

• Journal of Welding and Joining
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• 제23권5호
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• pp.20-24
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• 2005

Due to the difficulties associated with the supply of steel plates, hot rolled coil (Steel grade: SM490A) is considered fur structural materials in replace of the existing SWS50A-M1. However, it is found that SM490A exhibits a significant anisotropy in terms of impact energy with respect to transverse and longitudinal directions. In this study, an experimental investigation is carried out to examine the relationship between the anisotropy in impact values and the fatigue strengths of SM490A with respect to the rolling direction of test specimens. All test specimens failed around 1,500,000 cycles regardless of the test specimen direction. Therefore, it is found that the anisotropy in impact energy is not related to the fatigue strength of the materials considered in this study. However, the transverse direction specimen showed more rapid brittle fracture mode compared to that of longitudinal direction specimen, and this appears to be related to the lower impact values in transverse direction.

• 환경영향평가
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• 제16권6호
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• pp.503-510
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• 2007

Since 1990s many skyscrapers have been built in Seoul. However, gusty winds occur among tall buildings by descending turbulences due to the upper air blocking. This study aims to investigate the wind characteristics of skyscraper prevailing wind direction. In order to evaluate the building wind in this area, The wind speed and the wind direction were measured using propeller type RM-Young wind monitor in this study. The maximum wind speed was recorded by 15.1 m/sec and the main wind direction is WNW and NW. The ultimate purpose of this study is to figure out the phenomena of building wind impact and also to provide essential basic data for establishing proper guidelines in building wind impact assessment for skyscrapers in Korea.

• 한국운동역학회지
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• 제21권4호
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• pp.411-420
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• 2011

The purpose of this investigation was to determine whether correlations exist between balance and impact velocity, angular position, and maximum velocity of a club during drive swing. Twelve skilled golfers were recruited in this study. They were asked to perform ten swing trials and two trials were selected for analysis. Balance parameters were calculated via the force platform while kinematic variables were determined by using the Qualisys system. The results of the present study demonstrated that the average of COP velocity was faster in the medio-lateral direction rather than the anterio-posterior direction. Also, left foot's COP velocity and free torque were greater than the right foot's before impact. The range of the right foot's COP in the anterio-posterior direction before impact were correlated with the club velocity and angular position at impact. There was a negative correlation between the left foot's COP velocity before the impact and the velocity at impact. Additionally, the range and RMS of the left foot's free torque affected on the club angular position at impact and the maximum velocity at release, respectively. Finally, a negative correlation existed between the range of the right foot's free torque after the impact and club's maximum velocity at release.

• 환경영향평가
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• 제9권2호
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• pp.155-161
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• 2000

Environmental impact assessment(EIA), the only preventive system to manage development projects destroying the nature and ecosystem systematically, has been accomplished since the late 1970. EIA connotes intrinsic limits predicting uncertain future with the aid of present data. Furthermore, EIA has been used as not decision-making tools but regulatory means. Therefore, EIA has been criticized severely. In order to present direction of development of EIA, we analyzed problems of management of EIA, and concluded measures as follows are needed. 1. Control of investigation of environmental impact statements 2. Development of evaluating methods and publication 3. Fostering of institute for research and investigation of EIA 4. Construction of harmony of environment and development 5. Upgrade of state of proxy executing EIA.

• 제어로봇시스템학회논문지
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• 제5권8호
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• pp.955-960
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• 1999

This paper describes the effect of impact configurations on a single robot manipulator. The effect of different configurations of kinematically redundant arms on impact forces at their end effectors during contact with the environment is investigated. Instead of the well-known impact ellipsoid, I propose an analytic method on the geometric configuration of the impact directly from the mathematical definition. By calculating the length along the specified motion direction and volume of the geometry, we can determine the characteristics of robot configurations in terms of both the impact along the specified direction and the ability of the robot withstanding the impact. Simulations of various impact configurations are discussed at the end of this paper.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.69-73
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• 센서학회지
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• 제31권2호
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• pp.96-101
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• 2022

As the elderly population gradually increases, the risk of fatal fall accidents among the elderly is increasing. One way to cope with a fall accident is to determine the fall direction before impact using a wearable inertial measurement unit (IMU). In this context, a previous study proposed a method of classifying fall directions using a support vector machine with sensor velocity, acceleration, and tilt angle as input parameters. However, in this method, the IMU signals are processed through several processes, including a Kalman filter and the integration of acceleration, which involves a large amount of computation and error factors. Therefore, this paper proposes a machine learning-based method that classifies the fall direction before impact using IMU raw signals rather than processed data. In this study, we investigated the effects of the following two factors on the classification performance: (1) the usage of processed/raw signals and (2) the selection of machine learning techniques. First, as a result of comparing the processed/raw signals, the difference in sensitivities between the two methods was within 5%, indicating an equivalent level of classification performance. Second, as a result of comparing six machine learning techniques, K-nearest neighbor and naive Bayes exhibited excellent performance with a sensitivity of 86.0% and 84.1%, respectively.

• 한국건설관리학회논문집
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• 제23권2호
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• pp.95-101
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• 2022

본 연구는, 현재 대형 건설사에서 많이 채택하고 있는 벽식 구조에, 층간소음 효과가 우수한 라멘조 보를 직접 적용하여, 구조적 개선을 통한 효과적인 바닥충격음 저감 방안을 제시하고자 한다. 이를 위하여, 본 현장에서는 보 배근 방향의 변화와 스트럽 시공 유무를 통한 2가지의 구조적인 변화를 통하여, 가장 바닥충격음 저감에 효과적인 구조를 확인하고자 하였다. 현장 시험에 적용된 구조 개선은 총 6가지이며 ((1) 장변방향 보 배근, (2) 단변방향 보 배근, (3) 대각방향 보 배근, (4) 장변방향 보 배근과 스트럽 시공, (5) 단변방향 보 배근 및 스크럽 시공, (6)대각방향 보 배근 및 스트럽 시공), 이 슬래브들은 1차 테스트 (골조상태에서의 층간소음 측정)을 통하여, 가장 층간소음 저감 효과가 있는 보 배근 방향을 확인하였다. 현장 시험 결과, 가로방향의 보 배근과 스트럽 시공한 슬래브가 가장 층간소음 저감 효과가 뛰어난 것으로 나타났다. 이 슬래브가 일반 시공된 슬래브와 어떤 차이가 있는지 확인하기 위하여, 2차 테스트 (마감상태의 층간소음 측정)가 같은 층의 대조군과 비교함으로써 실행되었다. 이 결과, 최소1dB에서 최대 5dB정도로 현저하게 차이나는 것으로 나타났다. 결론적으로, 벽식구조에 라멘조 보와 스트럽을 적용한 구조는 단변방향 보다는 장변방향으로 배근하는 것이 효과가 훨씬 있는 것으로 나타났으며, 스트럽이 없는 보배근 보다는 스트럽이 있는 구조가 층간소음 저감에 효과가 있다고 여겨짐으로, 공동주택 벽식구조에 이러한 부분적인 구조 개선 적용이 가능하다고 본다.