• Journal of the Society of Naval Architects of Korea
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• v.55 no.4
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• pp.321-329
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• 2018

Resonance phenomena occurs at large vertical pump which is operating to cool down the hot steam using sea water in the power plant. To avoid the resonance, the natural frequency needs to be isolated about 20% from motor operating speed. Yet, excessive vibration occurs especially at low tide. At first, natural frequency of the whole pump system and each part is calculated using ANSYS. As it is revealed in the previous journal papers that only circular pipe part is related to resonance, the FSI technique is applied for free vibration analysis. The natural frequency is reduced to 60% (compared to that) of the frequency measured in air as it is similar to other published results. And the frequency obtained by finite element analysis is almost same to that obtained from modal test. Based on the accurate finite element model and analysis, design change is tried to avoid the resonance by changing the thickness of pipe and base supporting plate. In stead of doing optimization process, design sensitivity is computed and used to find such designs to avoid resonance.

• Journal of electromagnetic engineering and science
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• v.18 no.1
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• pp.1-6
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• 2018

In this study, the analytic expression for the positive/negative $n^{th}-Mode$ resonance frequency of an N unit cell composite right-/lefthanded (CRLH) transmission line is derived. To explain the resonance mechanism of the $n^{th}$ mode, especially for the negative mode, the current distribution of the N unit cell CRLH transmission line is investigated with a circuit simulation. Results show that both positive and negative $n^{th}$ resonance modes have n times current variations, but their phase difference is $180^{\circ}$ as expected. Moreover, the positive $n^{th}$ resonance occurs at a high frequency, whereas the negative $n^{th}$ resonance transpires at a low frequency, thus indicating that the negative resonance mode can be utilized for a small resonator. The correlation between the slope of the dispersion curve and the bandwidth is also observed. In sum, the balanced condition of the CRLH transmission line provides a broader bandwidth than the unbalanced condition.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.313-323
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• 2013

Offshore floating structures have so-called moonpool in the centre area for the purpose of drilling, installation of subsea structures, recovery of Remotely-Operated Vehicle (ROV) and divers. However, this vertical opening has an effect on the operating performance of floating offshore structure in the vicinity of moonpool resonance frequency; piston mode and sloshing mode. Experimental study based on model test was carried out. Moonpool resonance of floating offshore structure on fixed condition and motion free condition were investigated. And, the effect of cofferdam which is representative inner structure inside moonpool was examined. Model test results showed that Molin's theoretical formula can predict moonpool resonance on fixed condition quite accurately. However, motion free condition has higher resonance frequency when it is compared with that of motion fixed. The installation of cofferdam moves resonance frequency to higher region and also generates secondary resonance at lower frequency. Furthermore, it was found that cofferdam was the cause of generating waves in the longitudinal direction when the vessel was in beam sea.

• Journal of the Korea Society for Simulation
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• v.24 no.3
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• pp.45-54
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• 2015

This paper presents the influence of backlash can be greatly increased on the frequency response characteristic which is presented as the angular velocity of a motor to the motor input voltage, if the motor input voltage is adequately reduced. And, this paper verifies theoretically, analytically and experimentally the availability on the method of detecting the change of backlash magnitude by investigating on the change of the anti-resonance and resonance frequencies in the frequency response characteristic due to the change of backlash magnitude. The amount of change of anti-resonance frequency is more useful that of resonance frequency when detecting the change of backlash magnitude, because the change of anti-resonance frequency can be measured more stable. This paper also shows the sharp change of resonance frequency can be investigated when the motor input voltage is enough reduced. The work will be useful for the further research on the backlash estimation method of a servo system with a gear reducer.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.473-480
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• 2020

In this paper, we proposed a high frequency equivalent circuit considering parasitic impedance components for differential noise analysis on the input stage during DC-DC buck converter switching operation. Based on the proposed equivalent circuit model, we presented a method to measure parasitic impedance parameters included in DC bus plate, IGBT, and PCB track using the gain phase method of a network analyzer. In order to verify the validity of this model, a DC-DC prototype consisting of a buck converter, a signal analyzer, and a LISN device, and then resonance frequency was measured in the frequency range between 150 kHz and 30 MHz. The validity of the parasitic impedance measurement method and the proposed equivalent model is verified by deriving that the measured resonance frequency and the resonance frequency of the proposed high frequency equivalent model are the same.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.25 no.3
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• pp.125-130
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• 2019

Shock and vibration inputs are transmitted from the vehicle through the packaging to the fruit. Inside, these cause sustained bouncing of fruits against each other and container wall. These steady state vibration input may cause serous fruit injury, and this damage is particularly severe whenever the fruit inside the package is free to bounce, and is vibrated at its resonance frequency. The determination of the resonance frequencies of the fruit and vegetables may help the packaging designer to determine the proper packaging system providing adequate protection for the fruit, and to understand the complex interaction between the components of fruit when they relate to expected transportation vibration inputs. Instrumentation and technologies are described for determining the vibration response characteristics of the pears for exporting with frequency range from 10 to 200 Hz, sweep rate of 1 octave/min, sweep method of logarithmic up and down and acceleration levels of 0.2, 0.4, 0.6, 0.8 and 1.0 G considering the domestic transportation environment. The resonance frequency of the pears ranged from 49.04 to 87.16 Hz and the amplitude at resonance was between 0.96 and 4.02 G in test frequency band and acceleration level. The resonance frequency and amplitude at resonance frequency band of the pears decreased with the increase of the sample mass. The multiple nonlinear regression equations for predicting the resonance frequency of the pears were developed using the independent variables such as mass, input acceleration.

• Smart Structures and Systems
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• v.21 no.2
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• pp.151-161
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• 2018

A new type of cascade sandwiched piezoelectric ultrasonic transducer is presented and studied. The cascade transducer is composed of two traditional longitudinally sandwiched piezoelectric transducers, which are connected together in series mechanically and in parallel electrically. Based on the analytical method, the electromechanical equivalent circuit of the cascade transducer is derived and the resonance/anti-resonance frequency equations are obtained. The impedance characteristics and the vibrational modes of the transducer are analyzed. By means of numerical method, the dependency of the resonance/anti-resonance frequency and the effective electromechanical coupling coefficient on the geometrical dimensions of the cascade transducer are studied and some interesting conclusions are obtained. Two prototypes of the cascade transducers are designed and made; the resonance/anti-resonance frequency is measured. It is shown that the analytical resonance/anti-resonance frequencies are in good agreement with the experimental results. It is expected that this kind of cascade transducer can be used in large power and high intensity ultrasonic applications, such as ultrasonic liquid processing, ultrasonic metal machining and ultrasonic welding and soldering.

• Journal of Korea Multimedia Society
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• v.18 no.4
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• pp.541-545
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• 2015

Wireless power transmission which can transmit the electrical power through the air is the promise technology. In this paper, the effects of wireless power transmission using magnetic resonance method have been studied on coil material, resonance frequency, and antenna type. We have found copper tube as a coil material had the better characteristics than that of enameled wire, and the optimal resonance frequency was 13.6MHz in the range of from 1MHz to 20MHz. And the double square spiral type antenna as a load coil was the best. The power transmission distance by magnetic resonance method with 13.6MHz was 150 cm.

• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1711-1719
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• 2005

In an electro statically actuated nanoelectromechanical system (NEMS) resonator, it is shown that both the resonance frequency and the resonance quality (Q) factor can be manipulated. How much the frequency and quality factor can be tuned by excitation voltage and resistance on a doubly-clamped beam resonator is addressed. A mathematical model for investigating the tuning effects is presented. All results are shown based on the feasible dimension of the nanoresonator and appropriate external driving voltage, yielding up to 20 MHz resonance frequency. Such parameter tuning could prove to be a very convenient scheme to actively control the response of NEMS for a variety of applications.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.57-58
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• 2008

외부 자기장이 spin-flip field보다 작은 조건 하에서 마이크로 사이즈로 패턴된 synthetic antiferromanet의 ferromagnetic resonance frequency를 표현할 수 있는 이론식을 유도했다. 또한 유도된 이론식을 통해 synthetic antiferromagnet의 기하학적, 자기적 성질이 ferromagnetic resonance frequency가 미치는 영향에 대해 연구했다.