• 한국연소학회지
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• 제16권3호
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• pp.41-51
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• 2011

In this paper, we describe the behavior of two self-excitations in laminar attached free-jet flames under the influence of DC electric fields, one of buoyancy-driven and the other of diffusion-thermal instability, established from the horizontal and vertical injection. In the horizontal injection with removed buoyancy effect, oscillating flames with the frequency of 1.3 - 7.4 Hz were observed in a certain condition with Lewis number more than unity. On the other hand, it was appeared Lewis number induced self-excitation as well as buoyancy-driven self-excitation in the vertical upward injection with DC electric fields. This behavior had frequency range of 1.6 - 9.4 Hz and was exhibited to attribute the buoyancy effect. Finally, a well-defined division about two self-excitations having similar frequency range is briefly discussed.

• 대한기계학회논문집B
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• 제20권12호
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• pp.3980-3990
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• 1996

When a moist air is rapidly expanded in a supersonic nozzle, nonequilibrium condensation occurs at a supersaturation state. Condensation shock wave appears in the nozzle flow if the releasing latent heat due to condensation goes beyond a critical value. It has been known that self-excited oscillations of the condensation shock wave generate in an air or a steam nozzle flow with a large humidity. In the present study, the passive control technique using porous wall with a cavity underneath was applied to the condensation shock wave. The effects of the passive control on the steady and self-excited condensation shock waves were experimentally investigated by Schlieren visualization and static pressure measurements. The result shows that the present passive control is a useful technique to suppress the self-excited oscillations of condensation shock wave.

• 한국분무공학회지
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• 제27권3호
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• pp.134-143
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• 2022

When a recess is applied to a swirl coaxial injector that uses liquid and gas propellants, a self-pulsation phenomenon in which the spray oscillates at regular intervals may occur. The phenomenon is caused by the interaction between the liquid and gas propellants inside the injector recess region. The propellants' kinetic energies are expected to affect significantly the spray oscillation. Therefore, cold-flow tests using helium as a gas-simulating propellant were conducted and compared with the results of the previous study using air. Dynamic pressure was measured in the injector manifold and frequency characteristics were investigated through the fast Fourier transform analysis. In the experimental environment, the helium density was about seven times lower than the air density. Accordingly, the intensity of pressure fluctuations was confirmed to be greater when air was used. At the same kinetic energy condition, the perturbation frequency was almost identical in the low flow rate conditions. However, as the flow rate increased, the self-pulsation frequency was higher when helium was used.

• 대한전자공학회논문지SD
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• 제48권9호
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• pp.13-21
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• 2011

본 논문에서는 MEMS 용량형 각속도 센서용 프로그래머블 CMOS 인터페이스 회로를 제작하고, 이를 MEMS 센싱 엘리먼트와 결합하여 평가하였다. 본 회로는 10 bit 프로그래머블 캐패시터 어레이 를 이용한 전하 증폭기, 오프셋 미세 조정을 위한 9 비트 DAC, 출력 민감도의 미세 조정을 위한 10 비트 PGA를 내장하여, 오프셋 및 민감도 오차를 정밀 조정할 수 있다. 제작 결과 자동 이득 제어 회로를 포함한 자가 발진 루프의 정상 동작을 확인하였다. 오프셋 오차와 민감도 오차는 각각 0.36%FSO 와 0.19%FSO 로 측정되었으며, 잡음 등가 해상도와 바이어스 불안정도는 각각 0.016 deg/sec 와 0.012 deg/sec 으로 평가되었다. 본 회로의 조정 기능을 이용하여 MEMS 용량형 각속도 센서의 기생 용량으로 인하여 발생되는 출력 오프셋 및 출력 민감도의 산포를 감소시킬 수 있으며, 이는 센서의 양산성 및 수율 향상에 크게 기여할 수 있을 것으로 기대된다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.27-33
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• 2004

The Noise generation mechanisms of propane laminar premixed flames on a slot burner have been studied experimentally. The sound levels and frequencies were measured for various mixture flow rates (velocities) and equivalence ratios. The primary frequency of self-induced noise increases with the mean velocity of mixture as $f{\;}{\propto}{\;}U_f^{1.144}$ and the measured noise level increases with the mixture flow rate and equivalence ratio as $p{\;}{\propto}{\;}U_f^{1.7}$$F^{8.2}$. The nature of flame oscillation and the noise generation mechanisms are also investigated using a high speed CCD camera and a DSRL camera. The repetition of sudden extinction at the tip of flame is evident and the repetition rates are identical to the primary frequencies obtained from the FFT analysis of sound pressure signals. CH chemiluminescence intensities of the oscillating flames were also measured by PMT with a 431 nm(10 FWHM) band pass filter and compared to the pressure signals.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(2)
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• pp.77-80
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• 2002

In this paper, InP-based HBTs have been optimally designed by numerical simulation and fabricated by the self-aligned process. The structure of HBT was designed in terms of the current gain*f$_{max}$ for the base and f$_{T}$*f$_{max}$ for the collector. The designed structure produced the current gain of about 50 and the cutoff frequency and the maximum oscillation frequency of 87GHz and 2940Hz respectively. In addition, we present a study of the vertical and lateral etching of InP with the mask sides parallel to the principal crystallographic axes, [0101 and (001). This etching characteristics arc used to fabricate self-aligned HBT structures with reduced parasitic effects.s.s.s.

• 정보처리학회논문지D
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• 제13D권3호
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• pp.391-398
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• 2006

본 논문에서는 최근 많은 연구가 진행되고 있는 무선 센서 네트워크 분야에서 이동 센서 노드의 배치 알고리즘인 DSSA(Distributed Self Spreading Algorithm)와 TBDA(Tree Based Deployment Algorithm)을 모델링 하고, 이들 알고리즘의 안정성과 정확성을 널리 사용되고 있는 모델 검증 도구인 SPIN을 이용하여 검증한다. 그리고 두 알고리즘이 무선 센서 네트워크의 중요사항인 에너지 소비면에서 효율적으로 동작하는지 SPIN 검증 도구를 이용하여 비교분석하고, DSSA에서 발생하는 진동에 대한 보완점을 제시한다.

• 한국통신학회논문지
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• 제24권6B호
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• pp.1074-1079
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• 1999

155.52 Mbps STM-1급 디지털 통신용 고성능 CMOS 리시버 칩을 설계 제작하였다. 제작된 리시버는 전송선로의 단락 또는 송신 중단 등으로 인해 데이터신호가 입력되지 않거나, 정전 발생 또는 시스템의 유지보수 등으로 인해 전원이 차단되었다가 복구될 때에도 155.52 MHz의 클락 주파수를 유지하여 항상 안정된 동작을 할 수 있는 구조로 이루어진다. 이를 위해 설계된 회로는 PLL을 기본으로 한 데이터 및 클락 복원회로 외에 데이터 감시회로와 전원 감시회로도 내장한다. 측정 결과 제작된 IC는 데이터신호가 입력되는 정상적인 상황에서뿐만 아니라, 데이터신호가 입력되지 않는 비정상적인 상황하에서도 항상 155.52 MHz의 안정된 클락을 발생시키고 있음을 알 수 있었음, PLL 루프의 실효 지터도 23 ps로 우수한 특성을 나타내었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.21-24
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• 2008

The present study numerically investigates the glottal airflow characteristics as well as acoustic features of phonation fully coupled with dynamic behavior of vocal folds. The vocal folds are described by a low-dimensional body-covered model characterized by bio-mechanical parameters such as glottal width, vocal folds stiffness, and subglottal pressure. The flow in the vocal tract is modeled as an incompressible, axisymmetric form of the Navier-Stokes equations (INS), while the acoustic field is predicted by the linearized perturbed compressible equations (LPCE). The computed result shows that a two-mass model of vocal folds is sufficient to reproduce temporal variations in oral airflow and glottis motion produced by female speakers. It is also found that i) the glottal width has a significant effect on the amplitude of glottal flow, and thus on the amplitude of acoustic wave in the vocal tract, ii) the vocal fold tension is the main control parameter for the fundamental frequency of phonation, iii) the subglottal pressure plays an appreciable role on reproduction of the self-sustained oscillation of vocal folds, and iv) the strength of pulsating airflow and vortical structures are primarily affected by glottal width and subglottal pressure, and are closely related to pitch, loudness, and voice quality. Finally, more comprehensive explanation about the difference between one- and two-mass models is presented with discussion of effectiveness of vocal folds oscillation and voice quality.

• 한국연소학회지
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• 제20권1호
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• pp.32-42
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• 2015

The combustion instability was experimentally investigated in model gas turbine combustor with dual swirl burner. When such instability occurs, a strong coupling between pressure oscillation and unsteady heat release excites a self-sustained acoustic wave which results in a loud sound, and can even cause fatal damage to the combustor and entire system. In present study, to understand the combustion instability with a premixed mixture, the detailed periods of pressure and heat release data in unstable flame mode were investigated by various measurement methods at relatively rich condition and lean condition near flammable limits. Also, to prepare the utilization of synthetic natural gas (SNG) fuel in gas turbine system, an investigation was conducted using a simulated SNG including methane as a reference fuel to examine the effects of $H_2$ content on flame stability. These results provide that the instability due to flash-back behaviour like CIVB phenomenon occurred at rich condition, while the repetition of relighting and extinction caused the oscillation of lean condition near flammable limit. From the analysis of $H_2$ content effects, it is also confirmed that the instability frequency is proportional to the laminar burning velocity at both rich and lean condition.