• Journal of Hydrospace Technology
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• 제1권1호
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• pp.57-65
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• 1995

For the mechanism of ship capsizing, we can generally consider that it\`s caused due to pure loss of stability, parametric oscillation(low cycle resonance) of ship in waves and the broaching phenomena. Among them, low cycle resonance occurs due to the dynamic change of righting arm with respect to the relative position of ship to waves. The dynamic change depends on the encounter period of a ship in following waves. This paper discusses the following items : (1) An analytical expression of GZ curve varying with respect to the relative position of ship to waves, (2) Non-linear equation of motion describing low cycle resonance, (3) The effects of righting arm, stability range and encounter period on low cycle resonance.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2012년도 전기공동학술대회 논문집
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• pp.184-184
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• 2012

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering the range of MCR, however, the range is un-measurable. To resolve the measurement issue, this study shows the measuring method and the estimating method of whiling vibration by using resonance frequency of sub harmonic.

• 한국산학기술학회논문지
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• 제2권2호
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• pp.73-79
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• 2001

압전재료를 이용한 지능패널의 전달음 저감성능을 실험적으로 연구하였다. 제안된 압전지능패널은 압전 감지기와 작동기가 부착되어 있는 주구조물에 흡음재가 한 쪽면에 부착된 구조이다. 이는 저주파에서 능동적 방법과 고주파에서 수동적방법을 혼용한 개념이다. 이 개념을 증명하기 위하여 음향실험을 수행하였다. 음향실험을 위하여 음향터널을 설계, 제작하여 음향특성을 실험하였다. 음향 특성실험을 통하여 800 Hz가지 평면파특성을 나타내었다. 단일패널에 흡음재를 부착한 지능패널은 첫번째 공진주파수영역을 제외한 중주파수영역에서 뚜렸한 소음저감성능을 나타내었다. 첫번째 공진주파수에 대하여 반전회로를 이용한 능동제어를 수행하여 약 10 dB소음저감을 이루었다. 또한, 공기층을 갖는 이중지능패널에 대한 실험을 통하여 공진주파수에서 뿐만 아니라 넓은 영역에서 좋은 소음저감성능을 보였다. 수동적 방법과 능동적 방법을 혼용한 압전지능패널은 넓은 주파수 영역에서의 소온저감대책으로 유망한 기술이다.

• Transactions on Electrical and Electronic Materials
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• 제6권4호
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• pp.159-163
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• 2005

We analyzed the fault current limiting characteristics of a flux-lock type $high-T_c$ super­conducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element. However, the impedance of the flux lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field. From the experimental results, we investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred.

• 한국재료학회지
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• 제20권12호
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• pp.640-644
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• 2010

Information technology devices, such as cellular phones, MP3s and so on, due to restrictions of space, require thin and small micro-speakers to generate sound. The reduction of the size of micro-speakers has resulted in the decrease of sound quality, due to such factors as frequency range and sound pressure level. In this study, the acoustical properties of oval microspeakers has been studied as a function of pattern shape on the diaphragm. The other conditions of micro-speakers, except for the pattern, was not changed. When the pattern is present on the diaphragm and the shape of pattern was a whirlwind, the resonance frequency was reduced due to the decrease of tensile strength of diaphragm. The patterns presented in the semi-minor axis of diaphragm did not effect a change of resonance frequency. However, increasing the number of patterns in the semimajor axis of diaphragm became a reason for the decrease of resonance frequency on edge side. When the depth of pattern on edge side was increased, the resonance frequency was decreased due to reduction of geometrical stiffness. If the height of edge and dome were increased, the resonance frequency and geometrical stiffness rapidly increased. After reaching the maximum values, they began to decrease with the continuous increase of height.

• 대한의용생체공학회:의공학회지
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• 제36권6호
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• pp.241-250
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• 2015

Noninvasive temperature monitoring is feasible with Magnetic Resonance Imaging (MRI) based on temperature sensitive MR parameters such as $T_1$ and $T_2$ relaxation times, Proton Resonance Frequency shift (PRFs), diffusion, exchange process, magnetization transfer contrast, chemical exchange saturation transfer, etc. While the temperature monitoring is very useful to guide the thermal treatment such as RF hyperthermia or thermal ablation, the optimization of the MR thermometry method is essential because the range of temperature measurement depends on the choice of the measurement methods. Useful temperature range depends on the purpose of treatment methods, for example, $42^{\circ}C$ to $45^{\circ}C$ for RF hyperthermia and over $50^{\circ}C$ for thermal ablation. In this paper, MR thermometry methods using $T_1$ and $T_2$ relaxation times and PRFs-based MR thermometry are tried on a 3.0 T MRI system and their results are reported and compared. In addition, the scanning protocol and temperature calculation algorithms from $T_1$ and $T_2$ relaxation times and PRFs are optimized for the different temperature ranges for the purpose of RF hyperthermia and/or thermal ablation.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 1996년도 추계학술대회 초록집
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• pp.18-18
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• 1996

• 천문학회보
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• 제31권2호
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• pp.33-33
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• 2006

• 한국포장학회지
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• 제13권1호
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• pp.19-23
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• 2007

Shock and vibration inputs are transmitted from the transporting vehicle through the packaging to the fruit. The vibration causes sustained bouncing of fruits against each other and the container wall. The steady state vibration input may cause serous fruit injury, and the damage is particularly severe if the fruits are bounced at its resonance frequency. The determination of the resonance frequencies of the fruits and vegetables may help the packaging designer to determine the proper packaging system providing adequate protection for the fruits, and to understand the complex interaction between the components of the fruits when they relate to expected transportation vibration inputs. To analyze the vibration properties of the apples for optimum packaging design during transportation, random vibration tests were carried out. In the random vibration test, the resonance frequency and PSD of the packaged freight of apples in the test were in the range of 82 to 97 Hz and 0.0013 to $0.0021G^2/Hz$ respectively and the resonance frequency and PSD of the packaged apples in the test were in the range of 13 to 71 Hz and 0.0143 to $0.0923G^2/Hz$.

• 한국자기공명학회논문지
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• 제12권2호
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• pp.96-102
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• 2008

Direct quantification of methanol in polymer electrolyte membrane (PEM) by solid-state nuclear magnetic resonance (NMR) spectroscopy was studied and the methanol concentrations in PEM produced by crossover and diffusion were compared. The error range of the quantification was not smaller than ${\pm}15%$ and the amount of the methanol crossed over in our direct methanol fuel cells (DMFCs) was less than the methanol diffused to PEM. The methanol concentration in the PEM of the DMFC operated at different current densities were equivalent.