• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.80-86
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• 2010

This paper describes the development result of S-band Transmitter of STSAT-3 by satellite research center(SaTReC), KAIST. STSAT-3 has two kinds of communication channels, S- band for Telemetry & Command and X-band for mission payload. S-band Transmiiter(STX) consist of modulator, frequency synthesizer, power amp and DC/DC converter. The modulation scheme of STX is FSK(Frequency Shift Keying). The interface between spacecraft OBC and STX is RS-422. The STX is based on modular design. The RF output power of STX is 1.5W(31.7dBm) and BER of STX is under 1E-5. The Test of STX is completed successfully such as functional Test and environmental(vibration, thermal vacuum) Test.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.104-112
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• 2003

The in-duct acoustical sources of fluid machines are often characterized by the source impedance and strength using the linear time-invariant model. However, negative resistances, which are physically unreasonable, have been found throughout various measurements of the source properties in IC-engines and compressors. In this paper, the effects of the time-varying nature of fluid machines on the source characteristics are studied analytically. For this purpose, the simple fluid machine consisting of a reciprocating piston and an exhaust is considered as representing a typical periodic, time-varying system and the equivalent circuits are analyzed. Simulated measurements using the analytic solutions show that the time-varying nature in the actual sources is one of the main causes of the negative source resistances. It is also found that, for the small magnitude of the time-varying component, the source radiates large acoustic power if the piston operates at twice the natural frequency of the static system. or integral submultiples of that rate.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.5
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• pp.215-226
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• 2017

In this paper, an experimental study was carried out for vibration control of cable bridges with structurally flexible characteristics. For the experiment on vibration control, a model bridge was constructed by reducing the Seohae Grand Bridge and the shear type MR damper was designed using the wind load response measured at Seohae Grand Bridge. The shear type MR damper was installed in the vertical direction at the middle span of the model bridge, and dynamic modeling was performed using the power model. The tests of the vibration control were carried out by non-control, passive on/off control and Lyapunov control method on model bridge with scaled wind load response. The performance of the vibration control was evaluated by calculating absolute maximum displacement, RMS displacement, absolute maximum acceleration, RMS acceleration, and size of applied power using the response (displacement, acceleration, etc.) from the model bridge. As a result, the power model was effective in simulating the nonlinear behavior of the MR damper, and the Lyapunov control method using the MR damper was able to control the vibration of the structure and reduce the size of the power supply.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.228-231
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• 2022

Most CCTVs operated by public institutions for crime prevention and parking enforcement are located on roads. The angle of these CCTV's view is often changed for various reasons, such as bolt loosening by vibration or shocking by vehicles and workers, etc. In order to effectively provide AI services based on the collected images, the service target area(ROI, Region Of Interest) must be provided without interruption within the image. This is also related to the viewpoint of effective operation of computing power for image analysis. This study explains how to maximize the application of artificial intelligence technology by setting the ROI based on the marker on the road, setting the image analysis to be possible only within the area, and studying the process of finding the ROI.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.705-712
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• 2022

A sudden pressure drop caused by the pressure relief valve acts as a strong noise source and propagates the compressible pressure fluctuation along the pipe wall, which becomes a excitation source of Acoustic Induced Vibration (AIV). Therefore, in this study, the numerical methodology is developed to evaluate the reduction effect of compressible pressure fluctuation due to curved pipe in the pressure relief valve system. To describe the acoustic wave caused by density fluctuation, unsteady compressible Large Eddy Simulation (LES) technique, which is high accuracy numerical method, Smagorinsky-Lilly subgrid scale model is applied. Wavenumber-frequency analysis is performed to extract the compressible pressure fluctuation component, which is propagated along the pipe, from the flow field, and it is based on the wall pressure on the upstream and downstream pipe from the curved pipe. It is shown that the plane wave and the 1st mode component in radial direction are dominant along the downstream direction, and the overall acoustic power was reduced by 3 dB through the curved pipe. From these results, the noise reduction effect caused by curved pipe is confirmed.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.277-284
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• 2024

This study proposes a method to predict noise reduction based on noise-reduction measures, using harmonic response analysis, for transformer design. The dynamic elastic coefficients of the components comprising the actual transformer were determined by manufacturing the materials of the transformer components into simple-shaped specimens, followed by a comparison of the modes between the experiments and the analyses. A finite element model of the transformer was implemented, and harmonic response analysis was performed by deriving the exciting force of the transformer. Subsequently, the theoretical sound power level of the transformer was derived from the results of the harmonic response analysis. Finally, noise reduction measures were established, and the noise reduction amounts were compared between the experiments and the analyses, before and after applying the measures. Through the comparison and analyses of the noise reduction measures, it was confirmed that the trends in the experiments and analyses matched.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.68-72
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• 2008

Fiber-optic strain sensors based on Bragg reflection gratings produce the change of reflection spectrum when an external stress is applied on the sensor. To measure the Bragg reflection wavelength in high speed, an arrayed waveguide grating device is incorporated in this work. By monitoring the output power from each channel of the AWG, the peak wavelength corresponding to the applied strain could be obtained. To enhance the accuracy of the AWG wavelength interrogation system, a chirped fiber Bragg grating with a 3-dB bandwith of 5.4 nm is utilized. The high-speed response of the proposed system is demonstrated by measuring a fast varying strain produced by the damped oscillation of a cantilever. An oscillation frequency of 17.8 Hz and a damping time constant of 0.96 second are obtained in this measurement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.185-189
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• 2010

This study considered the feasibility of controlling the air concentration by oscillating flow in fuel cell channels. The fuel cell stack performance is largely influenced by the air concentration. If the air concentration is lower than 2.5 times the stoichiometric of the inlet air, the fuel cell stack performance seriously deteriorates because of air starvation. In this respect, optimizing the air concentration is crucially important to maximizing the fuel cell stack performance. In this work, the effects of oscillating actuation were studied to control the concentration. Studies have shown that there are two non-dimensional key parameters related to the frequency and oscillating amplitude. This paper presents how those parameters affect the performance of the stack.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1189-1194
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• 2011

The Maglev train is operated by levitating from a power of a large number of magnets and moving without direct contact to railway track so that reduces noise and vibration due to mechanical friction. Also, the Maglev passes sharp curves and steep hill without any difficulties. The Maglev has a potential to be an alternative transport system urban areas. For successful commercializing of Maglev, the organization of interface for safety and reliability of third rail system are one of the key considerations. Especially, the components of the third rail system, such as power rail, expansion joints, FRP section insulator, and supporter with epoxy insulator, should be durable, convenient for construction, and easy to maintenance. This paper analyzes the characteristics of the third rail system components and proposes organization of interface for system engineering. The operating tests of KIMM for the proposed third rail system verify the safety. Also, this paper analyzes the life cycle of the system components to improve the system reliability and evaluation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.553-558
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• 2011

This paper describes the development and test result of S-band Transmitter flight model(FM) of STSAT-3 by satellite research center(SaTReC), KAIST. The communication sub-system of STSAT-3 is consist of two different frequency band channels, S-band for Telemetry & Command and X-band for mission data. S-band Transmitter(STX) functionally made of modulator, frequency synthesizer, power amp and DC/DC converter. The transmission data is modulated by FSK(Frequency Shift Keying) and the interface between spacecraft sub-module and STX is RS-422 standard method. The FM STX is based on modular design. The RF output power of STX is 1.5W(31.7dBm) and BER of STX is under $1{\times}10^{-5}$ which meets the specification respectively. The FM STX is delivered Spacecraft Assembly, Integration and Test(AIT) level through the completion of functional Test and environmental(vibration, thermal vacuum) Test successfully.