• Tribology and Lubricants
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• v.30 no.1
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.87-95
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• 2012

This technical paper describes the analysis results of telemetry data for the initial activation of star trackers for an agile high accuracy low earth orbit satellite. The satellite was recently launched and is in the Launch and Early Operation Phases. It uses two SED36 star trackers manufactured by SODERN. The star tracker is separated by three parts, an optical head, an electronics box, and a baffle with maintaining optical head base plate temperature 20 degC in order to achieve the better performance in low frequency error. This paper presents the initial activation status, requirements and performance, anomaly occurrence, and noise equivalent angle performance analysis during the mission mode by processing the telemetry data.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.110.1-110.1
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• 2014

The optics of Space telescope is one of the major parts of space mission used for imaging observation of astronomical targets and the Earth. These kinds of space mission have a bulky and complex opto-mechanics with a long optical tube, but there are attempts have been made to observe a target with a small satellite in many ways. In this paper, we describe an optical design of a reflecting telescope for use in a CubeSat mission. For this design, we adopt the off-axis segmented method of astronomical observation techniques based on the Ritchey-Chr$\acute{e}$tien type telescope. The primary mirror shape is a rectangle with dimensions of $8cm{\times}8cm$, and a secondary mirror has dimensions of $2.4cm{\times}4.1cm$. The focal ratio is 3 which can obtain a $0.3{\times}0.2$ degree diagonal angle in a $1280{\times}800$ CMOS color image sensor with a pixel size of $3{\mu}m{\times}3{\mu}m$. This optical design can capture a ${\sim}4km{\times}{\sim}2.3km$ area of the earth's surface at 700 km altitude operation. Based on this conceptual design, we will keep trying to study more for astronomical observation with Attitude control system.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.1
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• pp.76-82
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• 2011

The thrust axis alignment of the launch vehicle is very important because the misalignment causes the unstable attitude control and results in mission failure. Generally, optical methods such as digital theodolite and laser tracker and mechanical method such as turn table method are used to align the thrust axis. This article deals with the simple method using inclinometer based on the gravitational direction. The inclinometer indicates zero degree when that is located on the perpendicular plate to gravitational direction. This method needs two inclinometer, such as standard and alignment ones and uses the angle difference as the reference data to adjust the TVC actuator offset.

• Wind and Structures
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• v.24 no.4
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• pp.333-350
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• 2017

Differing from the fixed-type, the dynamic motion of floating-type offshore wind turbines is very sensitive to wind and wave excitations. Thus, the sensing and monitoring of its motion is important to evaluate the dynamic responses to the external excitation. In this context, a monitoring system for sensing and processing the wind-induced dynamic motion of spar-type floating offshore wind turbine is developed in this study. It is developed by integrating a 1/00 scale model of 2.5MW spar-type floating offshore wind turbine, water basin equipped with the wind generator, sensing and data acquisition systems, real-time CompactRIO controller and monitoring program. The scale model with the upper rotatable blades is installed within the basin by means of three mooring lines, and its translational and rotational motions are detected by 3-axis inclinometer and accelerometers and gyroscope. The detected motion signals are processed using a real-time controller CompactRIO to calculate the acceleration and tilting angle of nacelle and the attitude of floating platform. The developed monitoring system is demonstrated and validated by measuring and evaluating the time histories and trajectories of nacelle and platform motions for three different wind velocities and for eight different fairlead positions.

• Fashion & Textile Research Journal
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• v.17 no.2
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• pp.258-264
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• 2015

This study provides abasis for the development of high functional cycle wear with clothing comfort and fitness for highschool boy cyclists by a comparison of the somatotype of highschool boys cyclists and general highschool boys. This study directly measured 44 anthropometric targeted cyclists across Korea. "The sixth national standard physical survey" data targeted 16 to 18-year-old male adolescents; subsequently, anthropometric measurement data was provided by 766 people for research. Highschool boy cyclists used t-test to compare the differences in body type. The results in this study are follows. Highschool boys cyclists(compared to regular highschool boys) indicated a great somatotype stature and weight. The differences in the cervical height and the acromion height results of, cyclist appeared smaller. Cyclists angle of shoulder was smaller. The upper body of highschool boys cyclist was greater than the difference between chest breadth and bust breadth with along biacromion length. The waist front length of the cyclist was a short cycle ride upon the attitude of the streamlined. Highschool boy cyclists indicated that the muscles of the arm portion was more developed compared to general highschool boys. The lower body had less abdominal fat with a significantly developed thigh and calf.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.2
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• pp.240-248
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• 2009

Modem version of supersonic jet fighter aircraft must have been guaranteed appropriate controllability and stability in HAoA(High Angle of Attack). The HAoA flight control law have two parts, one is control law of departure prevention and the other is control law of departure recovery support. The control laws of departure prevention for advanced jet trainer consist of HAoA limiter, roll command limiter and rudder fader. The control laws of departure recovery support are consist of yaw-rate limiter and MPO(Manual Pitch Override) mode. The guideline of pitch rocking using MPO mode is simple, but operating skill of pitch rocking is very difficult by the pilot with inexperience of departure situation. Therefore, automatic deep stall recovery system is necessary. The system called the "Automatic Pitch Rocker System" or APRS, provided a pilot initiated automatic maneuver capable of an aircraft recoveries in situations of deep stall, speed and altitude. This paper addresses the design and validation for APRS to recovery of an deep stall without manual pitch rocking by the pilot. Also, this system is designed to recovery of speed, attitude and altitude after deep stall recovery using ATCS (Automatic Thrust Control System) and autopilot. Finally, this system is verified by real-time pilot evaluation using HQS (Handling Quality Simulator).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.364-367
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• 2017

The basic design concept of the DACS(Divert and Attitude Control System) propellant is presented and the geometry optimization of the DACS propellant with limited outer diameter and maximum burning rate of the propellant is performed. Two-side burning surface conditions burned at the core and the one side of the propellant are applied to the propellant. And the optimized values for the radius of core, length of propellant, angle of end-side surface are obtained by the PSO algorithm. The direction for DACS propellant design is suggested by analyzing optimized design points for various burning rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.806-813
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• 2016

For satellite attitude control and maneuver, normally four reaction wheels are used through pyramid configuration. However, if satellite's moment of inertia is large or available reaction wheels' capability is small, we can consider using five reaction wheels. In this case, we should think the arrangement of wheels and their operation method. Active SAR satellite requires high agile maneuver about roll axis to achieve looking angle change. In this research, we study the operation method of five reaction wheels configuration for fast roll maneuver.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.760-766
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• 2018

Due to external disturbances on the satellite, unwanted momentum is accumulated on reaction wheels. To remove this momentum, three magnetic torquers which are installed along the satellite's axes are used. The magnetic torquers generated torque indirectly by interactions with the earth's magnetic field. Thus, during momentum dumping, we should consider both the magnetic torquer and the earth's magnetic field generated on the magnetic torquers at the same time. When low earth orbit satellite with high inclination angle holds nadir pointing attitude, weak earth's magnetic field is generated along the satellite's pitch axis. In this case, one magnetic torquer is overloaded and momentum dumping performance is degraded. This research will review the method to improve the momentum dumping performance by adjusting magnetic torquers arrangement.