하이브리드 로켓에서의 DC-shift 발생 특성

강동훈(Donghoon Kang),이창진(Changjin Lee) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.5

전형적인 하이브리드 모터의 연소 불안정 현상인 DC-Shift는 비선형적 특성을 갖는다. DC-Shift는 두 가지 형태로 나타나게 되는데, 압력이 급격하게 상승하는 양의 DC-shift와 연소 도중에 압력이 갑자기 감소하는 음의 DC-shift로 구분된다. 이 논문에서는 산화제 공급 유동 조건을 다양하게 변화시켜 음의 DC-shift 현상을 유도하고 산화제 공급 유동조건과 하이브리드 로켓이 갖고 있는 기본적인 주파수와 Helmholtz 주파수, 음향모드와의 공진을 유도하여 음의 DC-shift 현상의 발생 조건과 특징에 대하여 알아보았다. 실험결과 연소 중 수백 Hz 대역의 압력 주파수 이동을 확인하였으며, 음의 DC-Shift가 연소로 발생하는 주파수와 유동의 흐름으로 인한 주파수간 위상이 상호 감쇠되어 발생한 것으로 나타났다. 향후 연소 중 나타나는 주파수의 변화에 따른 DC-Shift 현상에 대해서는 계속 연구되어야 한다. Typical combustion instability such as DC-Shift found in the hybrid rocket motor is characterized by non-linearity. DC-Shift can occur in two different realizations. One is so-called a positive shift of measured DC voltage where the pressure increase suddenly. The other is a negative shift where the pressure drops abruptly. In the present work, specifically the negative DC-Shift was investigated to analyze the effect of oxidizer flow condition and the resonance between fundamental frequency and other ones, such as Helmholtz frequency, and acoustic frequency. Results show a peak frequency of several hundreds HZ shifts as combustion proceeds. A negative DC-shift was found as the result of phase cancellation between two dominant frequency, combustion frequency and flow related frequency. Still is it required to study further to identify the change of dominance of frequency during the combustion.

Frequency shift of a nanomechanical sensor carrying a nanoparticle using nonlocal Timoshenko beam theory

Zhi-Bin Shen,Dao-Kui Li,Dong Li 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.5

"The frequency shift of a nanomechanical sensor carrying a nanoparticle is studied. A bridged single-walled carbon nanotube (SWCNT)carrying a nanoparticle is modeled as a clamped micro-beam with a concentrated micro-mass at any position. Based on the nonlocal Timoshenko theory of beams, which incorporates size effects into the classical theory, the natural frequencies of the nanomechanical sensor are derived using the transfer function method. The effects of the mass and position of the nanoparticle on the frequency shift are discussed. In the absence of the nonlocal effect, the frequencies are reduced to the results of the classical model, in agreement with those using the finite element method. The obtained results show that when the mass of the attached nanoparticle increases or its location is close to the beam center, the natural frequency decreases, but the shift in frequency increases. The effect of the nonlocal parameter on the frequency shift is significant. Decreasing the length-to-diameter ratio also increases the frequency shift. The natural frequencies and shifts are strongly affected by rotary inertia, and the nonlocal Timoshenko beam model is more adequate than the nonlocal Euler-Bernoulli beam model for short nanomechanical sensors. The obtained results are helpful in the design of SWCNT-based resonator as nanomechanical mass sensor."

주파수 도약 시스템에서 Multi-Tone을 이용한 Frequency & Phase Shift Key Modulation 방법에 대한 연구

오경석(Kyung Seak Oh) 산업기술교육훈련학회 2014 산업기술연구논문지 (JITR) Vol.19 No.3

This paper, we designed a network in terms of bandwidth efficiency is primarily designed for non-performance of anti-jamming frequency-hopping system, which is mainly used in the method of single tone or two tone M-ary FSK, PSK modulation scheme to improve the limited bandwidth and power within the conventional M-ary FSK or PSK modulation method for high-speed data transmission Frequency & Phase Shift Keying Modulation method proposed and analyzed the operating principle.

Slip-Mode Frequency Shift 단독운전 검출 기법의 정상상태 전력 품질 개선

김동욱,김성민,Kim, Dong-Uk,Kim, Sungmin 한국전기전자학회 2018 전기전자학회논문지 Vol.22 No.3

계통 연계형 인버터는 단독운전 조건에서 반드시 전력 공급을 차단해야 한다. 이러한 이유로 분산 발전 시스템은 단독운전을 검출 기능을 반드시 가지고 있어야 한다. 분산 발전용 인버터에 적용되는 일반적인 방법 중에는 Slip-Mode frequency Shift (SMS) 단독운전 검출 기법이 있다. SMS 기법은 계통 전압의 주파수에 따라 무효 전력을 공급하여 단독운전 조건에서 계통 주파수를 허용 범위 밖으로 이동시키는 방법이다. SMS 기법은 안정적으로 단독운전을 검출할 수 있으며, 계통 전류에 고주파를 인가하지 않는다는 장점이 있으나, 무효 전류를 인가하기 때문에 계통 역률이 나빠져서 전력 품질의 저하를 가져온다. 본 논문에서는 계통 전원이 연결되어 있는 정상 조건에서 전력 품질 저하가 없는 수정된 SMS 기법을 제안한다. 600W 단상 인버터 실험을 통해 제안된 방법의 유효성을 검증한다. Grid-connected inverter is required to cut off the power supplied to the grid at the islanding condition, immediately. For this reason, an islanding detection is an indispensable function for grid-connected distributed generation system. Slip-Mode frequency Shift (SMS) islanding detection method is very popular method to determine the grid state. SMS method supplies the reactive power to the load according to the grid frequency. In the islanding condition of grid, this injected reactive power pulls out the grid frequency from the allowable range, then the inverter system can detect the islanding condition of the grid. The SMS method can detect the islanding state well and does not generate any harmonics of the grid current. However, the reactive power would be generated and the power quality is reduced even though the grid is not islanding condition, but normal condition. In this paper, a modified SMS method is proposed to remove the reactive power in the normal condition. The performance of the proposed method is evaluated by 600W single phase inverter experimental results.

Formulation of New Hyperbolic Time-shift Covariant Time-frequency Symbols and Its Applications

Iem, Byeong-Gwan The Acoustical Society of Korea 2003 韓國音響學會誌 Vol.22 No.e1

We propose new time-frequency (TF) tools for analyzing linear time-varying (LTV) systems and nonstationary random processes showing hyperbolic TF structure. Obtained through hyperbolic warping the narrowband Weyl symbol (WS) and spreading function (SF) in frequency, the new TF tools are useful for analyzing LTV systems and random processes characterized by hyperbolic time shifts. This new TF symbol, called the hyperbolic WS, satisfies the hyperbolic time-shift covariance and scale covariance properties, and is useful in wideband signal analysis. Using the new, hyperbolic time-shift covariant WS and 2-D TF kernels, we provide a formulation for the hyperbolic time-shift covariant TF symbols, which are 2-D smoothed versions of the hyperbolic WS. We also propose a new interpretation of linear signal transformations as weighted superposition of hyperbolic time shifted and scale changed versions of the signal. Application examples in signal analysis and detection demonstrate the advantages of our new results.

Extracting Frequency-Frequency Correlation Function from Two-Dimensional Infrared Spectroscopy: Peak Shift Measurement

곽경원 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

Two-dimensional infrared (2D-IR) spectroscopy can probe the fast structural evolution of molecules under thermal equilibrium. Vibrational frequency fluctuation caused by structural evolution produced the timedependent line shape change in 2D-IR spectrum. A variety of methods has been used to connect the evolution of 2D-IR spectrum with Frequency-Frequency Correlation Function (FFCF), which connects the experimental observables to a molecular level description. Here, a new method to extract FFCF from 2D-IR spectra is described. The experimental observable is the time-dependent frequency shift of maximum peak position in the slice spectrum of 2D-IR, which is taken along the excitation frequency axis. The direct relation between the 2D-IR peak shift and FFCF is proved analytically. Observing the 2D-IR peak shift does not need the full 2DIR spectrum which covers 0-1 and 1-2 bands. Thus data collection time to determine FFCF can be reduced significantly, which helps the detection of transient species.

A Frequency-Shift Keying Modulation Technique Using a Fractal Ring-Oscillator

Sung-Jin Kim,Won-Yong Choi,Kang-In Heo,Gyu Moon 보안공학연구지원센터 2015 International Journal of Multimedia and Ubiquitous Vol.10 No.11

A novel way of achieving the well-known FSK(Frequency-Shift Keying) modulation was introduced and verified. A simple form of CMOS ring-oscillator, that is generating a GHz level of frequency, was used as a base frequency generator. With its fractal structure, a local change in the oscillator will yield a global frequency change, which is to serve for the FSK. A local change is done with different number of inverting amplifiers in the ring oscillator with a multiplexer. Depending on how many cell changes, the frequency shifts are controlled and can be selected. The measured frequency difference between the shifts was from 9.2% up to 22.5%, in GHz range in CMOS SPICE simulations. Layout for CMOS implementation is also included.

Extracting Frequency-Frequency Correlation Function from Two-Dimensional Infrared Spectroscopy: Peak Shift Measurement

Kwak, Kyung-Won Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

Two-dimensional infrared (2D-IR) spectroscopy can probe the fast structural evolution of molecules under thermal equilibrium. Vibrational frequency fluctuation caused by structural evolution produced the time-dependent line shape change in 2D-IR spectrum. A variety of methods has been used to connect the evolution of 2D-IR spectrum with Frequency-Frequency Correlation Function (FFCF), which connects the experimental observables to a molecular level description. Here, a new method to extract FFCF from 2D-IR spectra is described. The experimental observable is the time-dependent frequency shift of maximum peak position in the slice spectrum of 2D-IR, which is taken along the excitation frequency axis. The direct relation between the 2D-IR peak shift and FFCF is proved analytically. Observing the 2D-IR peak shift does not need the full 2D-IR spectrum which covers 0-1 and 1-2 bands. Thus data collection time to determine FFCF can be reduced significantly, which helps the detection of transient species.

하이브리드 로켓의 DC-shift 불안정 발생 특성

강동훈(Donghoon Kang),이창진(Changjin Lee),몬킨우(Monkhinoo) 한국추진공학회 2009 한국추진공학회 학술대회논문집 Vol.2009 No.5

하이브리드 로켓의 연소 과정에서 DC-shift 현상을 관찰할 수 있다. 이와 같은 현상은 갑작스런 구조적 문제를 일으키거나 추력의 감소를 가져와 성능의 저하를 유발한다. DC-shift 현상에 대한 이해를 통해 하이브리드 로켓의 연소 안정의 조건을 알 수 있다. 이 논문에서는 음향모드와 와류유출주파수를 이용하여 DC-shift 현상을 유도하고 주파수의 변화에 따른 DC-shift 현상의 발생 조건과 세기에 대해서 알아보았다. DC-shift 현상에 대한 실험적 연구를 통하여 연소 안정의 조건을 정의하였다. DC-shift phenomenon can be observed in Hybrid rocket combustion. This phenomenon makes performance drop which is structure problem or reduce thrust. Understanding of DC-shift phenomenon, the conditions of the hybrid rocket combustion stability can be found. In this paper, the condition of DC-shift was found and made by using acoustic mode and vortex shedding frequency. The conditions of stable combustion was defined from the experimental study of DC-shift phenomenon.

뇌동맥류 파열 환자에서 경두개 Doppler검사에 대한 임상적 분석 : Preliminary Report

황용순,주진양,허승곤,이규창 대한신경외과학회 1990 Journal of Korean neurosurgical society Vol.19 No.10-12

The authors performed prospectively the transcranial Doppler monitoring of bilateral anterior and middle cerebral arteries in 15 patients with ruptured cerebral aneurysm. The entry criteria for the study were confined to the patients who were admitted within 3 days after bleeding and had clinical grades of Ⅰ, Ⅱ, or Ⅲ. The mean frequency shifts of bilateral anterior and middle cerebral arteries were increased immediately after ictus and showed continuous further elevation between the 3rd and 8th rupture days. After that, they normalized slowly. The increase of frequency shift preceded clinical ischemic symptoms and an early steep increase of frequency shift was correlated to a high chance for suffering delayed ischemic deficits. The thick clots in subarachnoid cisterns shown on CT scans taken within the third rupture day were correlated well to the severe increase of frequency shifts. The aggressive treatment was done on asymptomatic patients who showed relatively rapid increase of frequency shifts, and they had shown no or trasient mild ischemic symptoms.