• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.5
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• pp.410-418
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• 2018

This paper describes the design, analysis, and verification tests of the Dual-axis X-band antenna pointing mechanism(XAPM) that has been developed for the Earth observation mission at low Earth orbits. Based on the experience of development and operation of the similar system, we defined the main points and requirements of the system design and confirmed the characteristics of the system through the verification test of the launch and orbit environment test of the engineering qualification model. Through the characteristics and verification techniques of the system acquired during this process, improvement points of the later qualification model are derived.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.59-66
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• 2006

Acoustic cavity as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified in atmospheric temperature. First, harmful resonant frequency in a modeling chamber can be damped effectively by the installation of properly-tuned acoustic cavity. Besides, geometric effects of acoustic cavity on damping characteristics are analyzed and compared quantitatively. Satisfactory agreements have been achieved with linear acoustic analysis and experimental approach. Results show that the acoustic cavity of the largest orifice area or the shortest orifice length was the most effective in acoustic damping of the harmful resonant frequency. Finally, it is proved that an optimal design process is indispensable for the effective control of combustion instabilities.

• Journal of Biomedical Engineering Research
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• v.20 no.3
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• pp.315-321
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• 1999

The purpose of this study is to develop a mathematical model for system identification in order to predIct muscle force based on eledromyographic signal. Therefore, a finding of the relalionship between characteristics of electromyographic signal and the corre spondng muscle force should be necessiiry through dynamic, joint model. To develop the dynamic joint model, the upper limb mcludmg the wrist and elbow joint has been considered. The kinematic and dynamic data, such as joint angular displacement, velocity, deceleration along with the moment of inertla, required to establish the dynamic model has been obtained by electrical flexible goniometer which has two degree-of-frcedoms. ln this model, muscle force can be predicted only electromyographs through the relationship between the integrated lorce and the mtegrated electromyographic signal over the duration of muscle contraclion in this study.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.51-59
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• 2011

This paper is concerned with locomotion of dog-like quadruped robots that can adapt to various terrains, mainly dealing with implementation methods and characteristics of static and dynamic gaits. To this end, a 12-DOF robot is built in house, motional trajectories of its body and feet are generated mimicking biological life, and the corresponding leg joint angles are analytically obtained by inverse kinematics. Such joint angle data are then applied to the robot's ADAMS model for computer simulations so that the planned walk and trot gaits are both confirmed dynamically stable. However, contrary to the simulation results, previous trot patterns showed unstable behavior during experiments. This problem led us to analyze the reason, and in the course we discovered the importance of maximally utilizing the concept of WSM rather than ZMP and therefore reducing the gait period to secure the stability of dynamic gaits such as trot.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.207-214
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• 2001

Silica glass is a core material for optical fiber in optical telecommunications, but its centrosymmetry eliminates the second order nonlinearity. But it is experimentally well known that the space charge polarization induces the Second Harmonic Generation (SHG) when a strong DC voltage is applied to silica glass for a long period of time with metal blocking electrodes. In this report, the results of a theoretical calculation of the nonlinear optical property caused by the space charge polarization, and a model of a numerical analysis to predict the small chance in nonlinear optical property as functions of time and space are provided. Assuming that amorphous silica is a solid state electrolyte and sodium ion is the only mobile charge carrier, 'Finite Difference Method' was employed for modeling of numerical analysis. The distributions of the concentration of sodium ion and electric field as functions of a normalized length of the specimen and a normalized applied voltage were simulated.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.309-318
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• 2003

In this paper a 6 degree-of-freedom robot was studied for medical purpose. In the past the robot used for industry field was utilized for medical robot but in these days the robot used for rehabilitation. welfare, and service. This system was Proposed for a stroke patient or a patient who can not use one arm. A master-slave system was constructed to exercise either paralysis or abnormal arm using normal arms movement. Study on the human body motion result was applied to calculate a movement range of humans elbow and shoulder. In addition, a force-torque sensor is applied to estimate the rehabilitation extent of the patient in the slave robot. Therefore, the stability of the rehabilitation robot could be improved. By using the rehabilitation robot, the Patient could exercise by himself without any assistance In conclusion. the proposed system and control algorithm were verified by computer simulation and system experiment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.699-705
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• 2007

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test with PMMA/GOX in the hybrid rocket motor. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intented to simulate the process of fuel vaporization. LES technique was implemented to investigate both the flow characteristics near fuel surface and the subsequent evolution of turbulence modified by the wall blowing. Simple channel geometry instead of circular grain configuration was used for the investigation without chemical reactions in order to allow for a focused examination on the near-wall behavior at the Reynolds number of 22,500. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Journal of Navigation and Port Research
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• v.36 no.5
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• pp.357-361
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• 2012

Anemometer is a meteorological instrument that measures wind direction and wind speed in real time, and is mounted to the cranes that are used at ports, shipbuilding yards, off-shore structure, or construction sites that are influenced by wind, and it is used in conjunction with the safety system. Load cell-type anemometer measures the wind direction through the ratio of load between 4 positions by mounting the thin plate to 4 load cells, and measures wind velocity through the summation of loads. In this study, we compared and analyzed the results in the theoretic approach, analytic approach and experimental approach to derive the correlation between load ratio and wind direction. Wind direction was selected as the design variable, and selected 9 wind direction conditions from $0^{\circ}{\sim}90^{\circ}$ with $11.25^{\circ}$ space for analysis, and 10 wind direction conditions with $10^{\circ}$ space for experiment.

• Journal of Navigation and Port Research
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• v.44 no.6
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• pp.453-459
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• 2020

A sea trial of the speed performance test is the one of the most important means of verifying a ship's performance, and the International Organization for Standardization established a standard for this test in 2015. Environmental disturbances such as wind and waves are always present under real sea conditions, however, so it is impossible to accurately estimate delivered horsepower under ideal conditions. These disruptive influences also make it difficult to evaluate the positive effect of recently developed energy-saving devices. In this study, uncertainty analysis of improved speed performance was carried out using Monte Carlo simulation to confirm the energy-saving efficiency of a ship equipped with an air-lubrication system. The findings showed the average power saving to be 3.2%, with the expanded uncertainty of ± 2.7% at a 95% confidence level (k=2).

• Journal of Wetlands Research
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• v.15 no.1
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• pp.125-137
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• 2013

Global warming and climate change have influence on abnormal weather pattern and the rainstorm has a localized and intensive tendency in Korea. IPCC(2007) also reported the rainstorm and typhoon will be more and more stronger due to temperature increase during the 21st century. Flood Estimation Handbook(Institute of Hydrology, 1999) published in United Kingdom, in the case that the data period is shorter than return period, recommends the regional frequency analysis rather than point frequency analysis. This study uses Regional Climate Model(RCM) of Korea Meteorological Administration(KMA) for obtaining the rainfall and for performing the regional frequency analysis. We used the rainfall data from 58 stations managed by KMA and used L-moment algorithm suggested by Hosking and wallis(1993) for the regional frequency analysis considering the climate change. As the results, in most stations, the rainfall amounts in frequencies have an increasing tendency except for some stations. According to the A1B scenario, design rainfall is increased by 7~10% compared with the reference period(1970-2010).