• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.9
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• pp.1277-1283
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• 2013

In this paper, a novel voltage controlled oscillator(VCO) using CSRR loaded microstrip line for X-band RADAR is proposed. Using the microstrip line loaded CSRR inserted between the oscillator and buffer to the filter, the harmonic suppression has been improved. The measured results of the fabricated oscillator shows that its oscillation frequencies are from 9.28 to 9.39GHz according to the tuning voltage 0~10V, its output power level are about 16.6dBm at 9.35GHz. Compared with VCO using the conventional VCO, VCO using CSRR loaded microstirp, the harmonic suppression characteristic has been improved in 10.4dB

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.7-11
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• 2007

This paper presents a multiband octa-phase LC VCO for SDR receiver. Four identical LC VCOs are connected by using series coupling transistor to obtain the octa-phase signal and low phase noise characteristic. For a multiband application, a band tuning circuit that consists of a switch capacitor circuit and two MOS varactors is proposed. As the MOS switch is on/off state, the frequency range will be varied. In addition, two varactors make the VCO be immune to process variation of the oscillation frequency. The VCO is designed in 0.18-um CMOS technology, consumes 12mA current from 1.8V supply voltage and operates with a frequency band from 885MHz to 1.342GHz (41% tuning range). As driving sub-harmonic mixer, the proposed VCO covers 3 standards(CDMA 2000 1x, WCDMA, WiBro). The measured phase noise is -105dBc@100kHz, -115dBc@1MHz, -130dBc@10MHz for CDMA 2000 1x, WCDMA, WiBro respectively.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.330-343
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• 2016

This paper presents results of an experimental investigation of vortex-induced vibration (VIV) of a flexibly mounted and rigid cylinder with two-degrees-of-freedom with respect to varying ratio of in-line natural frequency to cross-flow natural frequency, $f^*$, at a fixed low mass ratio. Combined in-line and cross-flow motion was observed in a sub-critical Reynolds number range. Three-dimensional displacement meter and tension meter were used to measure dynamic responses of the model. To validate the results and the experiment system, x and y response amplitudes and ratio of oscillation frequency to cross-flow natural frequency were compared with other experimental results. It has been found that the higher harmonics, such as third and more vibration components, can occur on a certain part of steel catenary riser under a condition of dual resonance mode. In the present work, however, due to the limitation of a size of circulating water channel, the whole test of a whole configuration of the riser at an adequate scale for VIV phenomenon was not able to be conducted. Instead, we have modeled a rigid cylinder and assumed that the cylinder is a part of steel catenary riser where the higher harmonic motions could occur. Through the experiment, we have found that even though the cylinder was assumed to be rigid, the occurrence of the higher harmonic motions was observed in a small reduced velocity ($V_r$) range, where the influence of the in-line response is relatively large. The transition of the vortex shedding mode from one to another was examined by using time history of x and y directional displacement over all experimental cases. We also observed the influence of in-line restoring force power spectral density with $f^*$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.6
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• pp.682-690
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• 2012

In this paper, a highly linear self oscillating mixers(SOM) using second harmonic injections are presented. The H-slot defected ground structure(DGS) is designed as a balanced resonator for oscillation in the proposed SOM. Since the H-slot DGS resonator achieves a high Q factor, it is a suitable structure to provide low phase noise for the oscillator. The single balanced mixer is utilized in this work and it provides good LO-RF isolation since balanced LO signals are suppressed at the RF input port. In order to inject the second harmonic of the IF, we propose two different methods using feedback loops. In the first method, IF achieves a 3.08 dB conversion gain at 226 MHz with input power of -20 dBm at 5 GHz RF input signal. The IF achieves 2 dB conversion gain at 423 MHz with the input power of -20 dBm at 5.2 GHz RF input signal in the second method. The measured IMD3s are 61.8 dB and 65 dB for the each method. These SOMs present improved linearity compared to that without the second harmonic injection because IMD3s are improved by 18. dB and 21 dB for each method.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.510-521
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• 2001

A nonlinear acoustic instability of subcritical liquid-oxygen droplet flames burning in gaseous hydrogen environment are investigated numerically. Emphases are focused on the effects of finite-rate kinetics by employing a detailed hydrogen-oxygen chemistry and of the phase change of liquid oxygen. Results show that if nonlinear harmonic pressure oscillations are imposed, larger flame responses occur during the period that the pressure passes its temporal minimum, at which point flames are closer to extinction condition. Consequently, the flame response function, normalized during one cycle of pressure oscillation, increases nonlinearly with the amplitude of pressure perturbation. This nonlinear response behavior can be explained as a possible mechanism to produce the threshold phenomena for acoustic instability, often observed during rocket-engine tests.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.110-112
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• 2009

Transient acoustic pressure in the near field of an impacted plate carries information that can be utilized for recovering the impact force history. The inverse calculation approach using BEM-based NAH, which is conventionally used for time harmonic excitation, can be applied for reconstructing the transient waves using the principle of Fourier transform and spectral analysis. Then, using the recovered velocity in normal direction of the plate surface, the corresponding structural intensity can be obtained and the identification of input power can be performed. However, several manipulations should be given to overcome numerical artifacts, such as aliasing and erratic oscillation at discontinuity, and to suppress the effect of noise. Experiment using a simply supported plate is presented for demonstration purpose.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.49-56
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• 1987

The dynamic behaviour of a marine riser was studied theoretically and experimentally. In linear analysis, the natural frequencies and mode shapes of the riser were obtained from the experiment and they were found to be in good agreement with theoretical results by using a simple asymptotic formula. In nonlinear ananlysis including viscous drag and large displacement, a numerical-perturbation technique based on the derived linear asymptotic solutions is used to predict the displacements and stresses of the riser in harmonic motion. These results were also compared with experimental data and found to be in general in good agreement.

• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.3-4
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• 2017

컨버터 제어를 위한 피크 전류 모드는 기존의 전류 모드 제어 기법에 비해 빠른 응답과 간단한 구조로 인해 많은 컨버터 애플리케이션에서 사용된다. 그러나 듀티가 0.5를 초과하면, 서브 하모닉 발진이 전류에서 발생한다. 이러한 현상을 방지하기 위해 제어기를 안정적으로 동작 할 수 있도록 보상 기울기를 추가 한다. 그러나 기울기 보상의 방법은 구조를 복잡하게 만들고 출력 전압이 가변적 일 때 때때로 기울기를 변화시켜야 하는 문제가 있다. 따라서 본 논문에서는 기울기 보상 없이 새로운 하이브리드 모드 전류 제어 방법을 제안한다. 밸리 전류 모드에서 트레일 링 에지 변조를 사용하는 제안 된 방법에서, 서브 하모닉 발진 문제는 쉽게 해결 될 수 있다. 제안 된 제어기는 Psim 시뮬레이션에 의해 검증된다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.6 s.99
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• pp.706-711
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• 2005

Torsional oscillations of a system incorporating a Hooke's joint are investigated by studying a simple similar nonlinear 2-degree-of-freedom model, which has linear and quadratic nonlinear parametric excitations. The simple system is identified to have the possibilities of primary, sub harmonic and combination resonances. The case of simultaneous primary and combination resonances is selected for perturbation analysis to have the reduced amplitude-equations of motion. The same procedure is applied to the system incorporating a Hooke's joint.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.966-975
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• 2002

Acoustic behavior in baffled combustion chambers is numerically investigated by adopting linear acoustic analysis. Partial blade baffle, which is a variant of blade baffle, and hub-blade baffle with six blades are employed as baffle models. Through modal analysis, natural frequencies of each acoustic mode in baffled chambers are calculated and the reduction in natural frequencies caused by baffle installation is examined. Through harmonic analysis, acoustic pressure responses of each chamber to acoustic oscillating excitation are shown. The first tangential mode is found to be most sensitive to acoustic oscillation. Acoustic damping effect of baffle is quantified by damping factor. Damping effect of hub-blade baffle is the most appreciable and damping factor of partial blade baffle is much lower than that of blade baffle. Damping effect of six-blade baflle on the second tangential mode is as much as on the first tangential mode and hub-blade baffle can damp out appreciably the first tangential as well as the first radial mode with the aid of hub.