• Korean Journal of Applied Biomechanics
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• v.26 no.3
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• pp.243-248
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• 2016

Objective: The aim of this study was to determine the kinematical characteristics of somersault with twist in the Lou Yun and Akopian motions and to provide useful information to gymnastic athletes in men's vault. Method: The study subjects were 12 male adult top athletes. After 12 trials (7 Lou Yun and 5 Akopian trials) filmed by using two digital high-speed camcorders set at 90 frames/sec, kinematical data were collected through the direct linear transformation (DLT) method. The mean differences in biomechanical variables were compared during the second flight upward phase. The kinematic characteristics of somersault with twist in the Lou Yun and Akopian motions were identified. Results: In Lou Yun motion, the vertical release velocity through horse breaking was not difficult to obtain, so the athletes had enough time to prepare for the twist. Therefore, the Lou Yun motion has an advantage to make a cat twist in the pike posture. In the Akopian motion, obtaining the horizontal velocity through horse pushing was so easy that the Akopian athletes attained a large angular impulse and angular momentum. Therefore, the Akopian motion has an advantage to making a tilt twist in the body tilting posture. Conclusion: This study suggests that gymnastic athletes should control their body segment movements in order to increase the twisting angular velocity of the whole body, which requires regulation of the longitudinal moment of inertia of the body. Moreover, athletes should prepare for the shoulder and hip twists early in order to make the landing position in advance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.22-31
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• 2005

A design study was conducted for a new concept aircraft(Canard Rotor/Wing: CRW) that has the capability of dual mode flight, a rotorcraft and a fixed wing mode. The CRW can show a vertical take off/landing and a high speed/efficiency cruise performance simultaneously. It is not surprising to develop a new sizing code for this class of aircraft because conventional sizing codes developed solely for either the rotary wing or the fixed wing aircraft are not adequate to design a dual mode aircraft operated both by the rotary wing through tip jet effux and the fixed wing lift. Thus, a new design code was developed based on the conventional sizing code by adding some features including rotor performance, duct flow, and engine flow analysis, hence could eventually predict the performance of reaction driven rotor, the flight performance and the flight characteristics. The various design parameters were investigated to find their influences on the flight performance then, a small UAV(Unmanned Aircraft Vehicle) of 1500 lbs class was optimally designed to have minimum weight using the developed sizing code.

• Advances in aircraft and spacecraft science
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• v.1 no.2
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• pp.233-251
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• 2014

Each aircraft have to be certified for a specified level of impact energy, for assuring the capability of a safe flight and landing after the impact against a bird at cruise speed. The aim of this research work was to define a scientific and methodological approach to the study of the birdstrike phenomenon against several windshield geometries. A series of numerical simulations have been performed using the explicit finite element solver code LS-Dyna, in order to estimate the windshield-surround structure capability to absorb the bird impact energy, safely and efficiently, according to EASA Certification Specifications 25.631 (2011). The research considers the results obtained about a parametric numerical analysis of a simplified, but realistic, square flat windshield model, as reported in the last work (Grimaldi et al. 2013), where this model was subjected to the impact of a 1.8 kg bird model at 155 m/s to estimate the sensitivity of the target geometry, the impact angle, and the plate curvature on the impact response of the windshield structure. Then on the basis of these results in this paper the topic is focused about the development of a numerical simulation on a complete aircraft windshield-surround model with an innovative configuration. Both simulations have used a FE-SPH coupled approach for the fluid-structure interaction. The main achievement of this research has been the collection of analysis and results obtained on both simplified realistic and complete model analysis, addressed to approach with gained confidence the birdstrike problem. Guidelines for setting up a certification test, together with a design proposal for a test article are an important result of such simulations.

• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.78-83
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• 2010

In the present paper, a flap was optimized to maximize the lift. A 2-element fowler flap system was utilized for optimization with an initial shape of general aviation airfoil and a flap shape designed by Wentz. Response surface method and Hicks-Henne shape function were implemented for optimization. 2-D Navier-Stokes method was used to solve flow field around aGA(W)-1 airfoil with a fowler flap. Commercial programs including Visual-Doc, Gambit/Tgridand Fluent were used. Upper surface shape and the flap gap were optimized and lift for landing condition was improved considerably. The original and optimized flaps were tested in the KARI's 1-m low speed wind tunnel to examine changes in aerodynamic characteristics. For optimized flap tests, the similar trend to prediction could be seen but stall angle of attack was lower than what was expected. Also, less gap than optimized design delayed stall and produced better lift characteristics. This is believed to be the effect of turbulence model.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.109-112
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• 2008

The purpose of this study is to find out the characteristics of disasters caused by typhoons passing through the sea area around the Korean Peninsula. It analyzed two cases, that is, in WEST and EAST cases. These include the typhoons passing through the Yellow Sea, west of the Peninsula and East Sea, east of the Peninsula without landing on the Peninsula. FCM (Fuzzy Clustering Method) analysis was performed on typhoons affecting the Korean Peninsula from 1951 to 2006. The analysis shows that WEST case's cluster has the curved track of NE-S, and EAST case's cluster has the straight track of NE-SW. Typhoons that pass through the Yellow Sea have little change in frequency and the weak intensity. On the other hand, the frequency and the intensity of typhoons passing through the East Sea show the increasing trend. The characteristic of disasters by typhoons affecting the Korean Peninsula from 1973 to 2006 appears differently for each case: EAST cases caused significant damage in flooding, while WEST cases did damage in houses, ships, roads, and bridges. Rainfall amount and maximum wind speed data are analyzed in order to understand the impact of the typhoons, and the result indicates that the WEST cases are influenced by the wind, and East cases by precipitation. The result of this study indicates that the characteristic of disasters is distinctive according to the Typhoon's track. If applied to establish the disaster prevention plan, this result could make a contribution to the damage reduction.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.105-115
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• 2005

This study was investigated the kinematic factors of the last approach strides and. take off motion for the skill improving of BKH elite male athlete. 'The subjects chosen for the study were BKH and. KASZCZYK Emillian male athletes who were participated in 2003 Dae-Gu Universiad Games. Three high speed video cameras set in 60frames/s setting were used. for recording from the last approach strides to the apex position. After digitizing motion, the Direct Linear Transformation(DLT) technique was employed to obtain 3-D position coordinates, The kinematic factors of the distance, velocity and angle variable were calculated for Kwon3D 3.1. The following conclusions were drawn; 1. It showed longer stride length, as well as faster horizontal and lateral velocity than the success trial during the approach phase. For consistent of the approach rhythm, it appeared that the subject should a short length for obtain the breaking force by the lower COG during the approach phase. 2. The body lean angle showed a small angle by a high COG during the take-off phase. For obtain the vertical displacement of the COG and a enough space form the bar after take-off, it appeared that the subject should increase the body lean angle. 3. For obtain the vertical force during the takeoff phase, it appeared that the subject should keep straight as possible the knee joint. Therefor, the subject can be obtain a enough breaking force at the approach landing.

• Korean Journal of Applied Biomechanics
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• v.22 no.4
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• pp.387-394
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• 2012

The purpose of this study was to compare and analyze the finger pressure and kinematic variables in the forehand hairpin net shot between skilled elite players and less skilled recreational players. Eight elite players(age: $18.1{\pm}0.8yrs$, height: $176.8{\pm}1.5cm$, weight: $640.9{\pm}48.6N$) with minimum of 6 years of experience and eight recreational players(age: $27.9{\pm}1.6yrs$, height: $177.1{\pm}6.1cm$, weight: $820.5{\pm}62.8N$) with less than one year experience were recruited in this study. For each trial being analyzed, four critical instants were identified from the video recordings: Right heel contact1 (E1), Right toe-off (E2), Right heel contact2 (E3), and Shuttlecock Impact (E4). Each hairpin net shot was broken into consecutive phases: E1~E2 (Right Landing Phase: RLP), E2~E3 (Sliding Step Phase: SSP), and E3~E4 (Impact Phase: IP). Temporal parameters, shuttlecock speed, linear and angular kinematics of body segments, and finger pressures were computed for this study. The results showed that The finger pressure of the ring finger and the middle finger for the skilled group during an impact had significantly greater than those of unskilled group. It is possible that all fingers were not used in the same manner when the racket was gripped in forehand hairpin. The result also suggested that the ring finger and the middle finger pushed the racket from top to bottom while having the mid-phalanx and proximal phalanx of index finger as an axis.

• Journal of Advanced Navigation Technology
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• v.22 no.6
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• pp.491-499
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• 2018

Runway visual range (RVR), one of the important indicators of aircraft takeoff and landing, is affected by meteorological conditions such as temperature, humidity, etc. It is important to estimate the RVR at the time of arrival in advance. This study estimated the RVR of the local airport after 1 hour by upgrading the RVR estimation model using the proposed deep learning network. To this end, the advancement of the estimation model was carried out by changing the time interval of the meteorological data (temperature, humidity, wind speed, RVR) as input value and the linear conversion of the results. The proposed method generates estimation model based on the past measured meteorological data and estimates the RVR after 1 hour and confirms its validity by comparing with measured RVR after 1 hour. The proposed estimation model could be used for the RVR after 1 hour as reference in small airports in regions which do not forecast the RVR.

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.941-946
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• 2023

To improve the lift, cruise speed, and range of eVTOL aircraft, which are being considered as future transportation vehicles, this paper introduces the concepts of Tilt Rotor and Tandem Wing to the aircraft. We developed an aircraft and conducted flight experiments to obtain flight videos and flight logs. The results of the analysis of the flight videos and flight logs showed that the aircraft's moment was excessively forward and the attitude was not recovered. To address this problem, we modified the wing incidence angles and surface areas in XFLR5 to obtain the optimal pitching moment coefficients to ensure vertical stability. We then analyzed the redesigned aircraft, developed using CATIA, through XFLR5. The results of this study provide valuable insights, suggesting that the incorporation of Tilt Rotor and Tandem Wing designs can contribute to achieving stable pitching moment coefficients. This innovative approach offers a promising avenue to significantly enhance vertical stability in UAM vehicles, paving the way for future advancements in the field.

• Korean Journal of Applied Biomechanics
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• v.13 no.3
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• pp.253-264
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• 2003

This study aims at finding the structure of spike technique by analysing comparatively the spike action by excellent and by non-excellent players throughout the section from a flying jump to the time of landing for the correct analysis of spike action and tries to help athletes and coaches to execute a scientific training. For the objected person of this study, six of H College athletes three of excellent athletes and three of non-excellent athletes, presently registered as athlete with the Korea Volleyball federation) were chosen, and the factors of analysis were analysed upon performance time of action by section, human body centered displacement, change of articulation angle, speed change of articulation of the upper limbs, uniformity of the articulation of the upper limbs upon impact, etc. The conclusion of this study is as follow: 1. In the time required for taking action, it shows to take $1.067{\pm}0.057$ seconds for the group of excellent athletes and $1.034{\pm}0.033$ seconds for the group of non-excellent athletes. Although there was not big difference between two groups in the performance time of action, it showed that the group of excellent athletes takes longer compared to the group of non-excellent athletes. And it was found by the result of this study that the group of excellent athletes stays longer in the duration of flight. 2. In the displacements of horizontal movement and vertical movement, it was found that the group of excellent athletes have moved more than the group of non-excellent athletes in the horizontal movement of the center of human body 3. In the angles of wrist and knee, it was found that the excellent athletes have shown little than the non-excellent athletes in the entire sections, but that in the angle of elbow, the non-excellent athletes have shown bigger than the excellent athletes.. 4. In the speed of the articulation of the upper limbs upon impact, it was found that the group of excellent athletes have shown bigger than the group of non-excellent athletes, and that in the maximum value of the articulation of the upper limbs, the maximum value for the hand was indicated upon impact and that forearm and upper arm have shown the maximum value just before the impact. 5. In the uniformity of articulation of the upper limbs at the time of impact, the group of excellent athletes showed bigger than the group of non-excellent athletes in all the articulations.