• 한국운동역학회지
• /
• 제20권4호
• /
• pp.365-372
• /
• 2010

The purpose of this study were to analyze the changes in kinematic and kinetic parameters and to find biomechanical benefits of Nordic Walking and normal gait performed under the same velocity. Nine participants(age: $26.73{\pm}3.28$ year, height: $182.45{\pm}4.62\;cm$, weight: $76.59{\pm}6.84\;kg$) was chosen. The velocity of gait was set by 5.75 km/h which was made by a Nordic Walking professional. The data were collected by using VICON with 8 cameras to analyze kinematic variables with 200 Hz and force platform to analyze kinetic variables with 2000 Hz. The results of this study were as follows. First, when compared with Normal gait, Nordic Walking group showed decreased Plantarflexion angle and ROM. Second, Nordic Walking group showed decreased knee flexion angle and ROM. Third, Nordic Walking group showed increased hip joint movement. Fourth, Nordic Walking group showed higher active GRF but decreased loading rate from delayed Peak Vertical GRF time and increased impulse. Fifth, Nordic Walking group showed longer ground contact time. Through this study, we found that Nordic Walking showed higher stability and efficiency during gait than normal gait and that Nordic Walking may help people who have walking difficulties.

• 한국운동역학회지
• /
• 제33권4호
• /
• pp.137-146
• /
• 2023

Objective: The horizontal bar of gymnastics is fundamentally based on rotational movements. This study aimed to determine the effect of kinematics variables and sequence during horizontal bar performance (Kovacs, Tkatchev Stretched & Kolman) in gymnastic. Method: Four gymnastics athletes of the national team were participated in this study. All subjects were asked to perform the three types of horizontal bar skill. Simi marker-less cameras were used to collect the raw data (120 Hz). Kinematic variables (total time, interval, center of mass, height, angular velocity etc.) and sequence variables were calculated to examine the differences. Results: As a result, horizontal bar performance in gymnastic has special sequence that making the peak angular velocity from distal joint to proximal joint (knee-hip-shoulder). It is rare sequence that typical sport does not have. Conclusion: In field, gymnastic coaches and players should know the result that there is special sequence in horizontal bar performance. It could be very useful to teach and enhance their performance.

• 한국운동역학회지
• /
• 제15권1호
• /
• pp.29-44
• /
• 2005

The purpose of this study is to reveal the effects of two different kicks, the drop kick and the punt kick, into the kicking motion, through the kinetic comparative analysis of the kicking motion, which is conducted when one kicks a soccer goal. To grasp kinetic changing factors, which is performed by individual's each body segment, I connected kicking motions, which were analyzed by a two dimension co-ordination, into the personal computer to concrete the digits of it and smoothed by 10Hz. Using the smoothed data, I found a needed kinematical data by inputting an analytical program into the computer. The result of comparative analysis of two kicking motions can be summarized as below. 1. There was not a big difference between the time of the loading phase and the time of the swing phase, which can affect the exact impact and the angle of balls aviation direction. 2. The two kicks were not affected the timing and the velocity of the kicking leg's segment. 3. In the goal kick motion, the maximum velocity timing of the kicking leg's lower segment showed the following orders: the thigh(-0.06sec), the lower leg(-0.05sec), the foot(-0.018sec) in the drop kick, and the thigh(-0.06sec), the lower leg(-0.05sec), the foot(-0.015sec) in the punt kick. It showed that whipping motion increases the velocity of the foot at the time of impact. 4. At the time of impact, there was not a significant difference in the supporting leg's knee and ankle. When one does the punt kick, the subject spreads out his hip joint more at the time of impact. 5. When the impact performed, kicking leg's every segment was similar. Because the height of the ball is higher in the punt kick than in the drop kick, the subject has to stretch the knees more when he kicks a ball, so there is a significant affect on the angle and the distance of the ball's flying. 6. When one performs the drop kick, the stride is 0.02m shorter than the punt kick, and the ratio of height of the drop kick is 0.05 smaller than the punt kick. This difference greatly affects the center of the ball, the supporting leg's location, and the location of the center of gravity with the center of the ball at the time of impact. 7. Right before the moment of the impact, the center of gravity was located from the center of the ball, the height of the drop kick was 0.67m ratio of height was 0.37, and the height of the punt kick was 0.65m ratio of height was 0.36. The drop kick was located more to the back 0.21m ratio of height was 0.12, the punt kick was located more to the back 0.28m ratio of height was 0.16. 8. There was not a significant difference in the absolute angle of incidence and the maximum distance, but the absolute velocity of incidence showed a significant difference. This difference is caused from that whether players have the time to perform of not; the drop kick is used when the players have time to perform, and punt kick is used when the players launch a shifting attack. 9. The surface reaction force of the supporting leg had some relation with the approaching angle. Vertical reaction force (Fz) showed some differences in the two movements(p<0.05). The maximum force of the right and left surface reaction force (Fx) didn't have much differences (p<0.05), but it showed the tendency that the maximum force occurs before the peak force of the front and back surface (Fy) occurs.

• 수산해양기술연구
• /
• 제26권1호
• /
• pp.51-56
• /
• 1990

해저의 초음파산란층특성을 정량적으로 검토하기 위한 기초적 연구로서 선체의 동요로 인한 해저 Echo 신호의 파형과 진폭의 변동특성에 관하여 검토를 행한 결과를 요약하면 다음과 같다. (1) 해저 Echo 신호의 진폭은 1차 산란신호의 경우가 2차 산란신호보다 매우 불규칙하게 변동하였으나, 신호파형의 등가 Pulse 폭은 2차 산란신호가 1차 산란신호보다 약 2.4배 신장되어 수신되었다. (2) 해저산란파의 Echo Energy 변동은 Peak 진폭의 변동보다 매우 완만하고, 또 선체가 일정 경사각 범위 내에서 불규칙적으로 동요하는 경우, 선체동요에 기인하는 해저 Echo 진폭의 변동성분은 선체경사가 없는 경우에 대한 진폭성분과 서로 분리되어 나타났다. (3) 저질이 모래펄(MS)인 해저의 평균 Energy 산란강도는 -13.4 dB로서 평균 Peak 산란강도 -14.6 dB보다 1.2 dB 큰 값을 나타내었다.

• 천문학회보
• /
• 제35권1호
• /
• pp.28.2-28.2
• /
• 2010

We have investigated seven Extreme-Ultraviolet (EUV) bright points in the active region (AR 10926) on 2006 December 2 by the EUV imaging spectrometer (EIS) onboard Hinode spacecraft. We determined their Doppler velocities and non-thermal velocities from 15 EUV spectral lines (log T=4.7-7.2) by fitting each line profile to a Gaussian function. We present the Doppler velocity map as a function of temperature which corresponds to a different height. As a result, these active region bright points show two different types of characteristics. Type 1 bright point shows a systematic increase of Doppler velocity from -68 km/s (blue shift) at log T=4.7 to 27 km/s (red shift) at log T=6.7, while type 2 bright points have Doppler velocities in the range of -20 km/s and 20 km/s. Using MDI magnetograms, we found that only type 1 bright point was associated with the canceling magnetic feature at the rate of $2.4{\times}10^{18}$ Mx/hour. When assuming that these bright points are caused by magnetic reconnection and the Doppler shift indicates reconnection out flow, the pattern of the Doppler shift implies that type 1 bright point should be related to low atmosphere magnetic reconnection. We also determined electron densities from line ratio as well as temperatures from emission measure loci using CHIANTI atomic database. The electron densities of all bright points are comparable to typical values of active regions (log Ne=9.9-10.4). For the temperature analysis, the emission loci plots indicate that these bright points should not be isothermal though background is isothermal. The DEM analysis also show that while the background has a single peak distribution (isothermal), the EUV bright points, double peak distributions.

• Journal of Astronomy and Space Sciences
• /
• 제36권2호
• /
• pp.61-68
• /
• 2019

We have investigated the variations of sporadic E (Es) layer using the measurements of digisondes at Icheon ($37.14^{\circ}N$, $127.54^{\circ}E$, IC) and Jeju ($33.4^{\circ}N$, $126.30^{\circ}E$, JJ) in 2011-2018. The Es occurrence rate and its critical frequency (foEs) have peak values in summer at both IC and JJ in consistent with their known seasonal variations at mid-latitudes. The virtual height of the Es layer (h'Es) during equinox months is greater than that in other months. It may be related to the similar variation of meteor peak heights. The h'Es shows the semidiurnal variations with two peaks at early in the morning and late in the afternoon during equinoxes and summer. However, the semi-diurnal variation is not obvious in winter. The semi-diurnal variation is generally thought to be caused by the semi-diurnal tidal variation in the neutral wind shear, whose measurements, however, are rare and not available in the region of interest. To investigate the formation mechanism of Es, we have derived the vertical ion drift velocity using the Horizontal Wind Model (HWM) 14, International Geomagnetic Reference Field, and Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar-00 models. Our results show that h'Es preferentially occur at the altitudes where the direction of the vertical ion velocity changes. This result indicates the significant role of ion convergence in the creation of Es.

• 한국운동역학회지
• /
• 제25권1호
• /
• pp.1-10
• /
• 2015

Objective : The purpose of this study was to find some kinetic variable's relationships between personal records and low records in female high jump. Methods : Collected data of the subjects(N=8, ages: $25.5{\pm}1.85$, height: $173{\pm}5.83$, mass: $54.75{\pm}6.36$ personal record: $1.71{\pm}0.04$, low record: $1.62{\pm}0.03$) were used for the last three strides and take-off phase. Five video cameras set in 30frames/s were used for recording. After digitizing motion, the Direct Linear Transformation(DLT) technique was employed to obtain 3-D position coordinates. The kinematic and kinetic factors of distance, velocity, angle, impulse, jerk variables were calculated. A paired t-test was applied for the difference of variables between personal records and lower records and for correlation with performances and variables. The significance level was accepted at p<.05. Results : There was no relationship between pattern of stride and performance. However, rate of change of velocity was related with cental of mass height(CMH) at peak point(PP). Knee, hip, backward lean, foot plant, approach and take off angle showed no difference between best record and low record. Vertical impulse momentum also showed no difference between performances. Conclusion : According to a t-test result, there were significant differences in CMH at PP and jerk at touch down between best record and low record.

• 대한기계학회논문집B
• /
• 제26권6호
• /
• pp.893-901
• /
• 2002

Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670 mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer($\delta$=270 mm) was the natural turbulent boundary layer at the test section floor with fairly long developing length(18 m). The thin boundary layer($\delta$=36.5 mm) was generated on the smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity(3 ㎧) and the height of the model(40 mm) was 7.9$\times$10$^3$. The mean velocity vector fields and turbulent kinetic energy distributions were measured and compared. The effect of boundary layer thickness was clearly observed not only in the length of separation bubble but also in the location of reattachment point. The thinner the boundary layer thickness, the higher the turbulent kinetic energy Peak around the model roofbecame. It is strongly recommended that the height ratio between the model and the approaching boundary layer thickness should be encountered as a major parameter.

• 한국운동역학회지
• /
• 제27권1호
• /
• pp.9-18
• /
• 2017

Objective: The purpose of this study was to identify kinematic variables that govern successful performance and judges' scores and to establish correlative relationships among those of Yurchenko layout with a full twist in female vaults. Method: Four video cameras with sampling rate of 60 Hz collected 32 motion data of Yurchenko vaults from twenty-two female participants (age: $18.6{\pm}3.6years$, height: $153.0{\pm}6.5cm$, mass: $44.7{\pm}7.3kg$) during national competition. Posting processing and calculations of kinematic variables were performed in Kwon 3D XP and $Matlab^{(R)}$ programs. Correlation and regression analyses were applied to find the relationships between the obtained scores and kinematic variables. Deterministic model (Hay & Reid, 1988) was used to investigate the strength of correlative relationships among kinematic variables. Results: The obtained scores from the judges' decision were mainly affected by post-flight peak height, horse contact time, knee angle at landing, and horse takeoff angle. Strong blocking during horse contact was required to get successful performance and obtain high scores. Modified deterministic model showed that round-off entrance and takeoff angles and resultant velocity of the center of mass (CM) during the roundoff phase were the starting variables affecting performance in the following kinematics. Knee angle at landing, a highly influential variable on the obtained point, was only determined by judges' decision without significant correlative relationship with previous kinematic variables. Conclusion: The obtained scores highly depended on kinematic variables of post-flight and horse contact phases that were affected by those from the previous phases including round-off postures and resultant velocity of the body center of mass.

• 한국운동역학회지
• /
• 제14권1호
• /
• pp.13-26
• /
• 2004

The purpose of this study was to investigate the differences of the kinematical and the kinetical factors that calculated from preflight to preflight of salto forward straight 3/2 turn motion between skillers and less-skillers. four S-VHS video cameras operating at 60Hz were used to record the performances. Five elite male gymnasts were participated in this study as subjects. Three-dimensional coordinates of 21 body landmarks during each trial were collected using a Direct Linear Transformation method. The raw 3-D coordinates of the 21 body landmarks were smoothed using a second order lowpass, recursive Butterworth digital filter and a cutoff frequency of 10Hz. Load cells attached on the beneath of a board were used to attain the kinetic variables. It was found that the more angular momentum in the longitudinal axis, the less vertical velocity and these angular momentum effected the height of peak in the preflight. Also, it was revealed that the larger angular momentum in the medio-lateral axis was rather than it in the longitudinal axis to increase vertical height and rotation force of the body. For the reaction force of springboard, the vertical and the horizontal reaction force were 16.52BW and 3.45BW, respectively. It was found that the higher value of the vertical reaction force induced the faster vertical velocity and the higher an ar momentum. of the whole body center of gravity.