• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.184-189
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• 2006

Tumble flow test rig has been used as the useful tool in the developing intake system because major flow pattern induced by intake port of DOHC engine is tumble. Angular momentum of in-cylinder tumble flow can not be directly measured by impulse torque meter in the test rig like that of in-cylinder swirl flow due to rotational axis of the flow. Therefore the adaptor to transform tumble to swirl flow must be adapted in the test rig. In this study, using the commercial CFD code STAR-CD, we studied the effects on measured results due to the variation of the major design variables in the adaptor, tube length(L), tube diameter(D) and cylinder height(H). The effect of the attached angle($\theta$) of the test head to the adaptor also was simulated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.6
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• pp.957-962
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• 2013

This paper presents a performance testing device for safety fences of domestic professional baseball stadiums. Safety fences of professional stadiums have been fabricated and installed without adhering to any safety regulations, safety fences demonstrate critically low safety performances and many outfielders are severely injured every season. In this study, we designed and fabricated a performance testing device for safety fences and investigated its validity and reproducibility. A HIC (head injury criterion) was used for the statistical analysis of colliding data. We found that the optimal expulsion pressure and eliminated the accelerometer by replacing it with a velocity sensor using an estimation of the correlation between the momentum data obtained from velocity sensor and the impulse data from the accelerometer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.7
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• pp.764-774
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• 2008

A fire-out-of-battery(FOOB) mechanism, which is a new recoil technology, can reduce dramatically the level of a recoil force compared to the conventional recoil system. The FOOB mechanism pre-accelerates the recoil parts in direction opposite of conventional recoil before ignition. This momentum of the recoil parts due to pre-acceleration can reduce the firing impulse. In this paper, the dynamics of the recoil system with this FOOB mechanism is formulated and simulated numerically. The results of the simulation show that the FOOB system can reduce the recoil force and stroke compared to the conventional system under normal condition. When the fault modes happen, the FOOB system may not perform well and may be damaged seriously due to excessive recoil force and stroke. Hence, the control of the fault modes is necessary to achieve the normal operation of the FOOB system. The results that an additional MR damper enables the FOOB system to perform well under all firing condition.

• Korean Journal of Applied Biomechanics
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• v.23 no.2
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• pp.131-139
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• 2013

Naejirgi is one of the fastest, most forceful and most often being used kicks in Taekkyon games, The purpose of this study was to investigate kinetic factors on two types of Naejirgi kick, one of which uses knee bending of supporting leg and the other uses little it. 12 taekkyoners (11 males and one female) who are the students of Y University participated in this study. They have been practicing on Taekkyon for five years or more. Positions of CoM, the elapsed time of each phase, vertical ground reaction forces, joint moments and impulses of supporting leg were analyzed for this study. The results were as follows; in Naejirgi with knee bending of supporting leg than without knee bending of supporting leg, the vertical motion range of whole body CoM was larger during phase 2 and 3, the elapsed time of phase 4 were longer, players stayed longer in the nearest location to opponent, during phase 4 the vertical ground reaction forces of supporting foot were larger, and joint extension moments and angular impulses of supporting leg (especially knee) were larger. In conclusion supporting knee bending is not a useful strategy for Naejirgi, because players stay longer in the nearest position to opponent and consumed more muscle force and energy for producing the vertical momentum which is unnecessary for pushing down the opponent.

• Composites Research
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• v.22 no.4
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• pp.27-32
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• 2009

Characterisation of the stress-strain relationship as well as crashworthiness of cellular polymer was investigated under constant impact energy with different velocities, considering inertia and strain rate effects simultaneously during the impact testing. Quasi-static and impact tests were carried out for two different density (64 $kg/m^3$, 89 $kg/m^3$) cellular polymer specimens. Also, the equations, coupled with the Sherwood-Frost model and the Impulse-Momentum theory, were employed to build the constitutive relation of the cellular polymer. The nominal stress-strain curves obtained from the constitutive relation were compared with results from impact tests and showed to be in good agreement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.11
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• pp.753-760
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• 2019

Sparkjet actuator, also known as plasma synthetic jet actuator, which is a kind of active flow control actuator is considered as being high possibility for the supersonic flow control due to ejecting stronger jet compared to the other active flow control actuators. Sparkjet actuator generates high temperature and high pressure flow inside the cavity by using arc plasma and leads momentum by ejecting such flow through orifice or nozzle. In this research, numerical calculation of sparkjet actuator with respect to the location of electrodes which exists inside the cavity is conducted and the change of the performance of sparkjet actuator is suggested. As the location of electrodes goes closer to the bottom of the cavity, impulse is increased and the average pressure inside the cavity maintains higher. When the location of electrode is 25% and 75% of the entire cavity height, impulse is 2.515 μN·s and 2.057 μN·s, respectively. Each impulse is changed by about 9.92% and -10.09% compared to when the location of electrodes is 50% of the entire cavity height.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.28 no.4
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• pp.419-424
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• 1983

Tensile strength and shattering losses of rice grains in a binder harvest and in a free falling test were examined. Indica$\times$Japonica varieties, Milyang 23, Hangangchal, and Taebaek, and a Japonica variety, Jinheung were used for this study. The average tensile strength varied with varieties, showing 0.743N (Newton) in Milyang 23, 1.078N in Hangangchal, 1.573 N in Taebaek, and 1.775 N in Jinheung. Extrapolation of the average tensile strength for the zero field loss of grain indicated about 1.7 N. Moisture content of straw at the cutting position in a binder harvest was 76.0 to 86.7% in culm and 76.7 to 77.8% in leaf sheath. The percent loss of grains occurring in binder barvest in the field was equivalent to the degree of shattering in the panicle-falling test onto the concrete floor at the height of about 40cm. The grain shattering (Y) was closely related to the impulse (X), the change in momentum: Y=-25.73+4958.4X, ($r^2$=0.987) for Milyang 23, Y=-12.97+2258.3X, ($r^2$=0.979) for Hanagangchal, Y=-5.24+840.4X, ($r^2$ =0.976) for Taebaek. The tensile strengths of grains and their variance varied singnificantly yearly even in the same variety. The magnitude of year-variance was somewhat smaller for the easily shattering variety.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.703-712
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• 2004

A variant of the magnetoplasma jet engine (magjet) is here proposed for airbreathing flight in the hypersonic regime. As shown in Figure 1, the engine consists of two distinct ducts: the high-speed duct, in which power is added electromagnetically to the incoming air by a momentum addition device, and the fuel cell duct in which the flow stagnation temperature is reduced by extracting energy through the use of a magnetoplas-madynamic (MPD) generator. The power generated is then used to accelerate the flow exiting the fuel cells with a fraction bypassed to the high-speed duct. The analysis is performed using a quasi one-dimensional model neglecting the Hall and ion slip effects, and fix-ing the fuel cell efficiency to 0.6. Results obtained show that the specific impulse of the magjet is at least equal to and up to 3 times the one of a turbojet, ram-jet, or scramjet in their respective flight Mach number range. Should the air stagnation temperature in the fuel cell compartment not exceed 5 times the incoming air static temperature, the maximal flight Mach number possible would vary between 6.5 and 15 for a magnitude of the ratio between the Joule heating and the work interaction in the MPD generator varied between 0.25 and 0.01, respectively. Increasing the mass flow rate ratio between the high speed and fuel cell ducts from 0.2 to 20 increases the engine efficiency by as much as 3 times in the lower supersonic range, while resulting in a less than 10% increase for a flight Mach number exceeding 8.