• International Journal of Aeronautical and Space Sciences
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• v.11 no.4
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• pp.345-350
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• 2010

The repetitive vibrating action of an aerodynamic load causes an external fuel tank's horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.178-185
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• 1999

In tool condition monitoring systems, parameters should be set to a certain threshold. In many cases, however, the threshold is dependent on cutting conditions, especially the radial immersion ratio. In this presented is a method of on-line estimation of the radial immersion ratio in face milling. When a tooth finishes sweeping, a sudden drop of cutting force occurs. The force drop is equal to the cutting force that acting on a tooth at the swept angle of cut and can be acquired from cutting force signals in feed and cross-feed directions. Average cutting force per tooth period can also be calculated from cutting force signals in two directions. The ratio to cutting forces in two directions acting on a tooth at a certain swept angle of cut and the ratio of average cutting forces in two directions per tooth period are functions of the swept angle of cut and the ratio of radial to tangential cutting forces. Using these parameters, the radial immersion ratio is estimated. Various experiments are performed to verify the proposed method. The results show that the radial immersion ratio can be estimated by this method regardless of other cutting conditions.

• Journal of the Korean Society of Physical Medicine
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• v.6 no.2
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• pp.145-151
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• 2011

Purpose: The study was designed to investigate the effects of landing heights on muscle activities and ground reaction force during drop landing. Methods: Sixteen healthy adults were recruited along with their written informed consent. They performed a drop-landing task at the height of 20, 40, and 60cm. They completed three trials in each condition and biomechanical changes were measured. The data collected by each way of landing task and analyzed by One-way ANOVA. Ground reaction forces were measured by force flate, muscle activities measured by MP150 system. Results: There were significant differences in ground reaction forces, and significant increases in muscle activities of tibialis anterior, medial gastrocnemius and biceps femoris with landing heights. Conclusion: These findings revealed that heights of landing increases risk factors of body damage because of biomechanical mechanism and future studies should focus on prevention from damage of external conditions.

• Korean Journal of Applied Biomechanics
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• v.31 no.2
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• pp.113-118
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• 2021

Objective: The purpose of this study was to investigate differences of landing strategy between people with or without chronic ankle instability (CAI) during double-leg drop landing. Method: 34 male adults participated in this study (CAI = 16, Normal = 18). Participants performed double-leg drop landing task on a 30 cm height and 20 cm horizontal distance away from the force plate. Lower Extremities Kinetic and Kinematic data were obtained using 8 motion capture cameras and 2 force plates and loading rate was calculated. Independent samples t-test were used to identify differences between groups. Results: Compared with normal group, CAI group exhibits significantly less hip internal rotation angle (CAI = 1.52±8.12, Normal = 10.63±8.44, p = 0.003), greater knee valgus angle (CAI = -6.78±5.03, Normal = -12.38 ±6.78, p = 0.011), greater ankle eversion moment (CAI = 0.0001±0.02, Normal = -0.03±0.05, p = 0.043), greater loading Rate (CAI = 32.65±15.52, Normal = 18.43±10.87, p = 0.003) on their affected limb during maximum vertical Ground Reaction Force moment. Conclusion: Our results demonstrated that CAI group exhibits compensatory movement to avoid ankle inversion during double-leg drop landing compared with normal group. Further study about how changed kinetic and kinematic affect shock absorption ability and injury risk in participants with CAI is needed.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.47-55
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• 1997

Dynamic characteristics of the short circuit mode are investigated using the Volume of Fluid (VOF) method. When the initial molten drop volume, contact area and wire feed rate are given, rate change of the molten bridge profiles, pressure and velocity distributions are predicted. The electromagnetic force with proper boundary conditions are included in the formulation to consider the effects of welding current. It is found that the molten metal is transferred to the weld pool mainly due to the pressure difference caused by the curvatures in the initial stage, and electromagnetic force becomes dominant factor in the final stage of short circuit transfer. Necking occurs at the contact position between the molten drop and weld pool, and the initial molten drop volume and welding current have significant effects on break-up time.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.6
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• pp.739-748
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• 2004

A hybrid dust-collector combining a fabric filter with centrifugal force was developed to enhance the performance of the conventional fabric filter systems and its performances were evaluated to compare to that of the existing dust collector. The pressure drop rapidly increased with increasing the elapsed time and the face velocity in two filtration systems. But the increasing ratio of a hybrid dust-collector compare to the existing dust collector was lower. This results were confirmed from the performance such as cleaning interval, residual pressure drop and dust loading rate. The overall collection efficiency of the hybrid dust-collector was more than 99.6% and this showed a improvement of 0.6～2% than that of the existing dust collector. Especially, the fractional collection efficiency at the particle size of around 1${\mu}{\textrm}{m}$ is about 4% higher than that of the existing dust collector.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.84-91
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• 1997

The metal transfer phenomenon of the pulsed-GMAW is simulated by formulating the electromagnetic force incorporated with the Volume of Fluid algorithm. The free surface profiles, pressure and velocity distributions within the drop are computed numerically. Axial velocity and acceleration generated during peak current period are found to have a significant effect on drop detachment. Therefore, the accelerated inertia force becomes one of important factors affecting metal transfer in the pulsed-GMAW. When the pulse current parameters are selected properly, the molten drop is detached just after current pulse, and the operating range of the pulsing frequency increases with higher peak current and duty cycle. Calculated operating ranges show reasonably good agreements with the available experimental data.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.4
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• pp.148-155
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• 1998

It is commonly known that, in GMAW, the characteristics of metal transfer and the size of molten drop are highly dependent on the welding current. These changes in the characteristics of metal transfer has a considerable effect on the weld quality, and a lot of studies have been made on metal transfer modes for that reason. In this study, two cases were investigated; the one in which the metal transfer proceeds with gravitational force, surface tension, and no electromagnetic force, and the other in which the process has electromagnetic term in addition, where the current density in the fluid has been assumed to have Gaussian distribution on any given cross-section and it acts vertically. Using fluid flow analysis, this study has observed the whole process of the development and break-up of the molten drop, and it also showed that transitional processes, drop rate, and the drop size in each metal transfer mode can be estimated.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.2
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• pp.149-156
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• 2016

The spent fuel stored in the pool is vulnerable to external impacts, since the severe reactor conditions degrade the structural integrity of the fuel. Therefore an accident during shipping and handling should be considered. In an extreme case, the fuel assembly drop can be happened accidentally during handling the nuclear fuel in the spent fuel pool. The rod failure during such drop accident can be evaluated by calculating the impact force acting on the fuel assembly at the bottom of the spent fuel pool. The impact force can be evaluated with the impact velocity at the bottom of the spent fuel pool. Since fuel rods occupies most of weight and volume of a nuclear fuel assembly, the information of the rods are important to estimate the hydraulic resistance force. In this study, the hydraulic force acting on the $3{\times}3$ short rod bundle model during the drop accident is calculated, and the result is verified by comparing the numerical simulations. The methodology suggested by this study is expected to be useful for evaluating the integrity of the spent fuel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1121-1125
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• 2008

A development of landing gear drop test rig system for a small aircraft was studied and presented in this paper. Hydraulic actuators were considered in order to operate test system automatically and the wire winch system was applied to keep safety of test operators. This rig system was manufactured after checking the structural stability. Friction force measurement and drop velocity evaluation tests were done to confirm the confidence of test system. As a results of evaluation tests, it was confirmed that developed landing gear drop test system was adaptable.