• 한국운동역학회지
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• 제21권5호
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• pp.603-610
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• 2011

The long jump motions of 8 finalists in the women's long jump at the IAAF World Championships, Daegu 2011 were analyzed, and the kinematic characteristics of their techniques were investigated. The kinematic characteristics of the long jump motion of the 8 finalists were as follows. In the run-up phase, the length of the 2 stride was $108{\pm}6.92%$ that of the 3 stride. The length of the 1 stride was $91{\pm}5.78%$ that of the 2 stride. The change in the height of the center of gravity was $0.07{\pm}0.03$ m. The maximum velocity during the run-up phase was $9.44{\pm}0.13$ m at the 1 stride. In the take-off phase, the horizontal velocity, vertical velocity, reduction in horizontal velocity were $7.80{\pm}0.15$ m/s, $2.96{\pm}0.14$ m/s, and $1.64{\pm}0.19$ m/s, respectively. The minimum knee angle and take-off angle were $151{\pm}8.89^{\circ}$ and $20.7{\pm}1.03^{\circ}$, respectively. In the flight phase, the flight time and maximum height of the center of gravity were $0.78{\pm}0.03$ s, and $1.60{\pm}0.05$ m, respectively. In the landing phase, the landing length was $0.50{\pm}0.07$ m. The trunk angle, knee angle, and hip angle were $74{\pm}18.75^{\circ}$, $131{\pm}10.45^{\circ}$, and $82{\pm}9.03^{\circ}$, respectively. The kinematic characteristics of the motion of a good long jump were as follows. The reduction in the horizontal velocity in the take-off phase was minimized, and the maximum velocity of the run-up was maintained. The vertical velocity in the take-off phase was increased using a rapidly extended knee and high center of gravity.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2006년도 춘계 종합학술대회 논문집
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• pp.351-355
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• 2006

본 연구의 목적은 모든 하천에서 표면유속만을 이용하여 유량측정을 용이하게 할 수 있는 효과적이고 유용한 측정방법을 개발하는데 있다. 본 연구로 다음과 같은 중요한 결과를 얻었다. 1) 자연하천은 엔트로피 M값에 대응하여 평형상태를 유지하는 경향이 있으며, 2) 표면유속을 이용하여 산정된 계산치와 실측을 비교한 결과 상당히 좋은 일치를 보여주었으며, 3) 하천단면에서 최대유속이 발생하는 지점에서의 표면유속을 이용하여 유량을 산정하는 공식을 개발하였으며, 실측치와 비교한 결과 그 적용성을 확인하였다.

• 대한기계학회논문집B
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• 제41권5호
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• pp.311-320
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• 2017

액체가 부분적으로 채워져 있는 용기를 고속으로 이송시키면 슬로싱이 발생하므로 신속한 이송 및 조정 안정성을 위해 슬로싱을 억제할 필요가 있다. 본 연구에서는 사각용기를 수평방향으로 이송시킬 때 삼각형 속도 프로파일의 가속도 크기와 가감속 시간이 슬로싱에 미치는 영향을 수치해석적으로 연구하였다. 선행연구에서는 슬로싱의 1차 모드만을 고려하여 용기의 가감속 시간이 1차 고유 주기와 일치할 때 슬로싱이 상당히 억제됨을 보고한 바 있다. 반면 본 연구에서는 CFD 해석을 통해 슬로싱이 최소가 되는 가감속 시간을 찾고, 1차 모드 이외에 고차 모드를 함께 고려하여 이를 설명하였다. 또한, 질량과 스프링에 기반한 등가 모델을 이용한 해석을 수행하고 CFD 결과와 비교함으로써, 등가 모델의 정확성을 평가하였다.

• Reproductive and Developmental Biology
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• 제38권3호
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• pp.107-114
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• 2014

Oral exposure of humans by excess amounts of arsenic may cause disturbances of the reproductive system. In the present study, such exposure was modelled in rats, with the support of sperm principal parameters and histopathological observations. Male Sprague-Dawley rats were randomly divided into three groups where the group I was served as a normal control, group II was received sodium meta-arsenite as arsenic (10 mg/kg b.w/day) and a combination of sodium meta-arsenite and sodium selenite (3 mg/kg b.w/day) in group III. After 6 weeks, there was no significant change in testis weight and in total motility of all the three experimental groups, whereas, rapid moving spermatozoa, moderately moving spermatozoa and slow moving spermatozoa were significantly decreased in arsenic treated rats as compared to control rats. The other sperm principal parameters like progressiveness, average path velocity, straightness linear velocity (VSL), curvilinear velocity (VCL), straightness, linearity sperm head elongation ratio, area, linearity amplitude of lateral head department (ALH) and beat cross frequency (BCF) were found to be reduced in arsenic intoxicated rats. These results are not correlated with the histological studies. On oral administration of selenium ameliorated the adverse effects of arsenic as compared to arsenic alone treated rats. Our findings clearly demonstrate that administration of selenium could prevent some of the deleterious effects of arsenic in the testis.

• 한국운동역학회지
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• 제21권5호
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• pp.621-629
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• 2011

The purpose of this study was to analyze the kinematics of the women's triple jump event at the 2011 Daegu World a Chmpionships by comparing them to those of the 2009 Berlin World Championships. The kinematic data were gathered from two steps before take off to the landing using a 7-camera panorama system. The data were then divided into 3 phases for each of the 8 participants. Similar average results were found the final contestants in the Daegu and Berlin championships, 14.58 m and 14.51 m, respectively. The first step had a relatively short length percentage (29%) compared to the hop and jump (36% and 35%, respectively). At the take off, the horizontal velocity was the lowest for the step, followed by the hop and jump. These results were different from the results for the men, who had an order of hop, step, and jump. Overall, in a comparison of the Daegu and Berlin participants, the vertical speed at take off for the three events was reduced compared to the horizontal speed.

• 국제초고층학회논문집
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• 제12권2호
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• pp.129-136
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• 2023

Natural ventilation has proven to be an effective passive strategy in improving energy efficiency and providing healthy environments. However, such a strategy has not been commonly adopted to tall office buildings that traditionally rely on single-skin façades (SSFs), due to the high wind pressure that creates excessive air velocities and occupant discomfort at upper floors. Double-skin façades (DSFs) can provide an opportunity to facilitate natural ventilation in tall office buildings, as the fundamental components such as the additional skin and openings create a buffer to regulate the direct impact of wind pressure and the airflow around the buildings. This study investigates the impact of modified multi-story type DSFs on indoor airflow in a 60-story, 780-foot (238 m) naturally ventilated tall office building under isothermal conditions. Thus, the performance of wind effect related components was assessed based on the criteria (e.g., air velocity and airflow distribution), particularly with respect to opening size. Computational fluid dynamics (CFD) was utilized to simulate outdoor airflow around the tall office building, and indoor airflow at multiple heights in case of various DSF opening configurations. The simulation results indicate that the outer skin opening is the more influential parameter than the inner skin opening on the indoor airflow behavior. On the other hand, the variations of inner skin opening size help improve the indoor airflow with respect to the desired air velocity and airflow distribution. Despite some vortexes observed in the indoor spaces, cross ventilation can occur as positive pressure on the windward side and negative pressure on the other sides generate productive pressure differential. The results also demonstrate that DSFs with smaller openings suitably reduce not only the impact of wind pressure, but also the concentration of high air velocity near the windows on the windward side, compared to SSFs. Further insight on indoor airflow behaviors depending on DSF opening configurations leads to a better understanding of the DSF design strategies for effective natural ventilation in tall office buildings.

• 대한약학회:학술대회논문집
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• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
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• pp.317.2-318
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• 2003

The current study was performed to observe the effect of Sun Ginseng (SG) on hemodynamics such as blood flow rate (BF), blood flow velocity (BV), heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP), and body temperature (BT) in healthy young men. This is a randomized, single-blind study observed during 6 hrs after orally single administration of SG. (omitted)

• Steel and Composite Structures
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• 제42권3호
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• pp.397-405
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• 2022

The existing researches on the dynamics of the fluid-conveying pipes only focus on stability and vibration problems, and there is no literature report on the wave propagation of the fluid-conveying pipes. Therefore, the purpose of this paper is to explore the propagation characteristics of longitudinal and flexural waves in the fluid-conveying pipes. First, it is assumed that the material properties of the fluid-conveying pipes vary based on a power function of the thickness. In addition, it is assumed that the material properties of both the fluid and the pipes are closely depended on temperature. Using the Euler-Bernoulli beam equation and based on the linear theory, the motion equations considering the thermal-mechanical-fluid coupling is derived. Then, the exact expressions of phase velocity and group velocity of longitudinal waves and bending waves in the fluid-conveying pipes are obtained by using the eigenvalue method. In addition, we also studied the free vibration frequency characteristics of the fluid-conveying pipes. In the numerical analysis, we successively studied the influence of temperature, functional gradient index and liquid velocity on the wave propagation and vibration problems. It is found that the temperature and functional gradient exponent decrease the phase and group velocities, on the contrary, the liquid flow velocity increases the phase and group velocities. However, for vibration problems, temperature, functional gradient exponent parameter, and fluid velocity all reduce the natural frequency.

• 한국수자원학회논문집
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• 제33권2호
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• pp.169-179
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• 2000

이 연구에서는 1995년부터 1997년까지 금강수계 강경지점에서 유속계로 측정한 유속자료를 분석하여 자연하천의 연직방향 유속분포특성을 규명하였다. 또한, 현장유속 측정조건이 불량하여 다점법으로 유속분포를 측정하기 곤란한 경우, 간단하게 표면유속만을 측정하여 상대깊이별 유속을 추정할 수 있는 연직 유속분포식을 유도하였다. 2차 포물선의 유속분포식은 통계적으로 매우 안정적이고, 표면유속과 바닥유속 등과 고도의 유의성을 보였다. 2차 포물선식의 상수 및 계수와 표면유속과의 상관관계를 구하였으며, 실측 검정자료에 적용한 결과, 유속분포특성을 잘 반영하는 것을 확인할 수 있었다. 연직 유속분포식으로 추정된 유속은 실제수심을 적용하여 평균유속과 유량을 결정할 수 있으며, 이는 또한 하천의 오염물질이동 등 수질해석에 적용할 수 있을 것이다.

• 한국기계가공학회지
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• 제18권6호
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• pp.45-54
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• 2019

In this study, we analyze the rattle noise of a power takeoff (PTO) driveline and develop a PTO driveline resonance model. We measured the rattle noise of the PTO driveline on the output shaft and, by analyzing the rattle noise in the time domain, we determine that the engine expansion stroke period matches the sound pressure of rattle noise. This finding helped us demonstrate that the rattle noise is caused by the collision between the PTO driving gear and the gear driven by the engine expansion stroke; the torsional vibration caused by this collision is affected by the angular velocity fluctuation of the PTO drive shaft. By measuring the angular velocity of the PTO drive shaft, we confirm that the angular velocity fluctuation of the engine flywheel tends to excessively amplify the PTO drive shaft angular velocity fluctuation. We conclude that the resonance, which occurs when the operating frequency of the engine is close to the natural frequency of the tractor power transmission system, causes the excessive angular velocity fluctuation of the PTO drive shaft. We performed a modal analysis of the PTO driveline resonance and, using the characteristic equation, we show that the resonance occurs when the engine rotation speed is close to 850 rpm, which matches the natural frequency of the PTO driveline.