• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2120-2125
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• 2005

The principal idea of vibration isolation is to filter out the response of the system over the corner frequency. The isolation objectives are to transmit the attitude control torque within the bandwidth of the attitude control system and to filter all the high frequency components coming from vibration equipment above the bandwidth. However, when a reaction wheels or control momentum gyros control spacecraft attitude, vibration inevitably occurs and degrades the performance of sensitive devices. Therefore, vibration should be controlled or isolated for missions such as Earth observing, broadcasting and telecommunication between antenna and ground stations. For space applications, technicians designing controller have to consider a periodic vibration and disturbance to ensure system performance and robustness completing various missions. In general, past research isolating vibration commonly used 6 degree order freedom isolators such as Stewart and Mallock platforms. In this study, the vibration isolation device has 3 degree order freedom, one translational and two rotational motions. The origin of the coordinate is located at the center-of-gravity of the upper plane. In this paper, adaptive notch filter finds the disturbance frequency and the reference signal in filtered-x least mean square is generated by the notch frequency. The design parameters of the notch filter are updated continuously using recursive least square algorithm. Therefore, the adaptive filtered-x least mean square algorithm is applied to the vibration suppressing experiment without reference sensor. This paper shows the experimental results of an active vibration control using an adaptive filtered-x least mean squares algorithm.

• Composites Research
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• v.28 no.4
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• pp.212-218
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• 2015

A large composite spar was manufactured using an automatic fiber placement (AFP) machine. To verify its structural performance, the weakest part of the structure, which is called 'corner radius', was tested under bending and examined by finite element analysis. Since the application of AFP machine to composite structure fabrication is still in early stage in Korea, this paper presents the summary of whole process for manufacturing composite spar using AFP machine from mandrel design and analysis to verification test. The deflection and stress by mandrel weight and AFP machine force, thermal deformation and natural frequency were all examined for mandrel design. The target structure was composite C-spar and cured in an autoclave. Test results were compared with nonlinear finite element analysis results to show that the structure has the strength close to the theoretical value. It was confirmed that the corner radius of the spar manufactured by AFP process showed deviation less than 20% compared with first ply failure strength. The results indicate that the AFP technology could be used for large scale composite structure production in the near future.

• Journal of the Korean Geophysical Society
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• v.6 no.1
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• pp.25-29
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• 2003

We suggest a method that vectorially composes 3-component earthquake records in the frequency domain, to reduce the uncertainties in the analysis of the Fourier amplitude spectrum. The use of the Fourier amplitude spectrum composed from 3 components has two advantages. First, it provides a more accurate estimate of seismic moment by eliminating the vector-partition term that appears in individual component. Second, it provides more accurate estimates of seismic moment, corner frequency, high-frequency decay constant($χ$) .etc., by enhancing the shape of the Fourier amplitude spectrum. The latter is especially useful in the analysis of small earthquakes with low signal-to-noise ratios.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.5 s.143
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• pp.528-533
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• 2005

A mono-static high frequency acoustic target strength analysis scheme was developed for underwater targets, based on the far-field Kirchhoff approximation. Au adaptive triangular beam method and a concept of virtual surface were adopted for considering the effect of hidden surfaces and multiple reflections of an underwater target, respectively. A test of a simple target showed that the suggested hidden surface removal scheme is valid. Then some numerical analyses, for several underwater targets, were carried out; (1) for several simple underwater targets, like sphere, square plate, cylinder, trihedral corner reflector, and (2) for a generic submarine model, The former was exactly coincident with the theoretical results including beam patterns versus azimuth angles, and the latter suggested that multiple reflections have to be considered to estimate more accurate target strength of underwater targets.

• Journal of the Korean earth science society
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• v.29 no.2
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• pp.117-127
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• 2008

Source parameters for forty four earthquakes which occurred in and around the Korean Peninsula were determined and the relations between them were studied. Snoke's method (Snoke, 1987) was applied in determining the corner frequencies and seismic moments. In general, the source parameters estimated at different stations for an earthquake show different values. These disagreements have been interpreted as originating, in principle, from an inadequate consideration of the source radiation pattern and direction dependent attenuation and amplification. The comer frequencies and seismic moments were averaged to exclude the such directional effects. Other source parameters were estimated from the mean corner frequency and seismic moment. The static stress drops, determined in this study, tend to be independent of seismic moment for events greater than a specific magnitude. For earthquakes with a size less than about $1.0{\times}10^{22}$ dyne-cm (nearly same as $M_L = 4.0$), the stress drop tends to decrease with the decreasing moment. This fact suggests a breakdown of the scaling law of source parameters in earthquakes below the threshold magnitude.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1308-1315
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• 2009

A full-polarimetric scatterometer(HPS: Hongik Polarimetric Scatterometer) for X-band is designed, fabricated, and verified using the theoretically well-known point-targets in this paper. The X-band full-polarimetric scatterometer consists of an OMT(Orthogonal-Mode Transducer)+horn antenna, the angle control part for the OMT+horn antenna, a transmitter/receiver with a network analyzer and a frequency-conversion circuitry, and a movable support of these parts. We use an inclinometer sensor to control the vertical and horizontal incidence angles. The full polarimetric data can be obtained because of the polarization switches and the OMT. The accuracy of the scatterometer system is verified by measuring the polarimetric RCS(Radar Cross Section) of one of the theoretically well-known point-targets, i.e., a corner reflector.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.258-261
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• 2012

Helicopter-borne FMCW radar altimeter obtains the altitude information using the beat frequency between the transmitted and reflected signal from the nadir direction. However, the altitude error may exist when the strong echoes are received from the large RCS at the off-nadir direction because of the wide beamwidth of the altimeter antenna. In this paper, in order to investigate the effect of the altitude error due to the large RCS around the off-nadir direction, the reflected signals were measured by using the corner reflectors displaced on the several reference ground positions, and the acquired signals were analyzed and compared in the spectral domain. The analysis results can be used for the improvement of the altitude accuracy in the radar altimeter.

• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.289-292
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• 2009

In this paper, an optimum design center frequency proposes portable RFID reader antenna that is 920MHz frequency using the Taguchi's Method. Proposed antenna is cut corner of opposite angle and it's structure that have slots in four sides microstrip patch of a perfect square shape. This slot structure can miniaturize microstrip patch antenna and confirmed through an experiment that size of antenna about 18% decreases than structure that slot does not exist. Because compact antenna that have structure of slot changes according to complex design variables, analysis and experimental design for minimization of experiment number of times are required for optimum antenna design. In this research, designed antenna that have optimum structure when introduce and designs table of orthogonal arrays of the Taguchi's Method been experimental design that can minimize analysis and experiment number of times, achieve responsiveness analysis of main elements and analyzes the effect and minimizes design repeat with analysis result. Presented experiment result about antenna special quality that permittivity is 4.4 and manufactures to board of Epoxy 3.2T.

• Phonetics and Speech Sciences
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• v.9 no.1
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• pp.49-53
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• 2017

Formant frequencies depend on the position of tongue, the shape of lips, and larynx. In the auditory system, the external ear canal is an open-end resonator, which can modify the voice characteristics. This study investigates the effect of the real ear on formant frequencies. Fifteen subjects ranging from 22 to 30 years of age participated in the study. This study employed three corner vowels: the low central vowel /a/, the high front vowel /i/, and the high back vowel /u/. For this study, the voice of a well-educated undergraduate who majored in speech-language pathology, was recorded with a high performance condenser microphone placed in the upper pinna and in the ear canal. Paired t-test showed that there were significant difference in the formant frequencies of F1, F2, F3, and F4 between the free field and the real ear. For /a/, all formant frequencies decreased significantly in the real ear. For /i/, F2 increased and F3 and F4 decreased. For /u/, F1 and F2 increased, but F3 and F4 decreased. It seems that these voice modifications in the real ear contribute to interpreting voice quality and understanding speech, timbre, and individual characteristics, which are influenced by the shape of the outer ear and external ear canal in such a way that formant frequencies become centralized in the vowel space.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.546-552
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• 2012

This paper is a study on squeal noise simulation under the consideration of temperature and pressure dependent material properties of friction material. For this, data of pressure and temperature dependent material properties of lining is achieved by using lining data base and exponential curve fit. Complex eigenvalue analysis is performed for predicting squeal noise frequency and instability and chassis dynamo test is performed for achieving squeal noise frequency, sound pressure level, occurrence temperature & pressure. Initial multi models are composed for considering complex interface conditions such as pad ear-clip, piston-housing and guide pin-torque member. The simulation result of base models is compared with the test result. Squeal noise simulation under the consideration of temperature and pressure dependent material properties of friction material is performed and analyzed using multi models. And additional condition is disc material property variation. Entire simulation conditions are combined and analyzed. Finally, this paper proposes direction of the warm squeal noise model.