• Title/Summary/Keyword: 모드 불안정성

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Flow Visualization by Light Emission in the Post-chamber of Hybrid Rocket (광도측정에 의한 하이브리드 로켓 후연소실의 유동 가시화)

  • Park, Kyung-su;Choi, Go Eun;Lee, Changjin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.43 no.8
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    • pp.677-683
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    • 2015
  • Hybrid rocket combustion displays low frequency instability(LFI, 10~30Hz) at a certain condition. Vortex shedding in the post-chamber is suspected to cause the occurrence of LFI. This study focused on the visualization of flow image using light emissions from high temperature combustion gas. Results shows that combustion pressure oscillates at a frequency of about 18 Hz, which is in phase with oscillations of light emission. Since LFI is not a property of thermo-acoustic instability, this result suggested there exists a physical coupling of pressure fluctuations with light emissions proportional to chemical reaction. Also POD analysis shows that dominant symmetric spatial modes in the stable combustion shift suddenly into asymmetric spatial pattern with the appearance of LFI. Especially, the appearance of mode 3 is a typical change of flow dynamics in unstable combustion representing a rotational fluid motions associated with vortex shedding.

Stabilization and characterization of a 10 GHz harmonically mode-locked Er-doped fiber ring laser by suppression of relaxation oscillation (완화진동억압을 이용한 10 GHz 고조모드잠금된 고리형 어븀첨가 광섬유 레이저의 출력 안정화 및 특성 측정)

  • 장지웅;이유승;전영민;임동건
    • Korean Journal of Optics and Photonics
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    • v.13 no.1
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    • pp.58-64
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    • 2002
  • Using Mach-Zehnder type intensity modulator, we stabilized a 10 GHz harmonically mode-locked dispersion-compensated fiber ring laser using a feedback controlling system, and we measured its stability. The laser was stabilized for more than 16 hours by controlling the cavity length to suppress the relaxation oscillation frequency component which had caused the laser output instability. The ms timing jitter and ms amplitude noise were measured to be 260-524 fsec and 4~11.5%, respectively, and BER test measurement showed a value of 10$^{-13}$ .

An Analysis on Combustion Instability in Solid Rocket Motor of 230mm Grade (230mm급 고체 추진기관의 연소불안정 거동 현상 분석)

  • Kwon, Tae-Hoon;Rho, Tae-Ho;Suh, Hyuk
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.05a
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    • pp.177-180
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    • 2009
  • A Possibility of combustion instability on longitudinal mode has a high level at large scale of L/D. Solid propellant has a metal particle and a grain of control to pressure oscillation. Solid rocket motor in slotted-tube grain controls pressure oscillation of longitudinal mode. If slot length is shot, pressure oscillation of longitudinal mode is amplified by cylinder part after middle phase of total burn time. A study has analyzed pressure oscillation of longitudinal mode at spectrum and acoustic modal analysis at pressure of result on static firing test.

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An Experimental Study on the Flame Dynamics in the Model Combustor with V-gutter type Flameholder (V-gutter 형 보염기가 장착된 모델 연소기 내에서 발생하는 화염 동특성 연구)

  • Song, Jin-Kwan;Jeong, Chan-Young;Yoon, Young-Bin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.11a
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    • pp.379-385
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    • 2010
  • Mechanism of combustion frequencies occurring during combustion is experimentally investigated in a model combustor with V-gutter flameholder. The combustor has a long duct shape with a cross section area of $40{\times}40mm$. The v-gutter type flameholder with 10, 12, 14mm width is mounted at the side wall of combustor. CNG were used as fuel, and the fuel was injected transversely into air crossflow. It is found that combustion frequencies were considered as first longitudinal mode caused by combustor geometry. And it is found that flameholder length affects the flame holding range. Also, it is observed first longitudinal pressure oscillations make significant changes of flame structure.

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10 GHz wavelength tunable mode-locked filber ring laser configured with all polarization maintaining fiber (편광유지 광섬유로 구성된 10 GHz 파장가변 모드록킹 광섬유 고리형 레이저 제작 및 특성연구)

  • 김봉규;김명욱;전영민;이정찬;김상국;최상삼
    • Korean Journal of Optics and Photonics
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    • v.9 no.4
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    • pp.270-273
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    • 1998
  • We have demonstrated the wavelength tunable ultrashort pulse fiber ring laser proposed the novel method for measuring the cavity loss from relaxation oscillation frequency and the pump power. To suppress the polarization instability the laser cavity is configured with polarization maintaining fibers and to control the center wavelength a 2.4 nm bandwidth tunable wavelength filter was inserted in the cavity. The laser has 8 picosecond pulse width, 10 GHz repetition rate and 1.2 mW average power in 1530-1560 nm operation range.

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Linear Stability Analysis for Combustion Instability in Solid Propellant Rocket (고체추진 로켓의 선형 안정성 요소에 대한 연구)

  • Kim, Hakchul;Kim, Junseong;Moon, Heejang;Sung, Honggye;Lee, Hunki;Ohm, Wonsuk;Lee, Dohyung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.5
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    • pp.27-36
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    • 2013
  • Linear stability analysis for combustion instability within a cylindrical port of solid rocket motor has been conducted. The analysis of acoustic energy has been performed by a commercial COMSOL code to obtain the mode function associated to each acoustic mode prior to the calculation of stability alpha. An instability diagnosis based on the linear stability analysis of Culick is performed where special interests have been focused on 5 stability factors(alpha) such as pressure coupling, nozzle damping, particle damping and additionally, flow turning effect and viscous damping to take into account the flow and viscosity effect near the fuel surface. The instability decay characteristics depending on the particle size is also analyzed.

Low Frequency Squeal Noise Reduction using Mode Participation Factor in Complex Eigenvalue Analysis (복소고유치해석에서 모드기여도 인자를 이용한 저주파 스퀼소음 저감)

  • Park, Jeong Min;Kim, Hyun Soo;Yoon, Moon Young;Boo, Kwang Seok;Kim, Heung Seob
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.3
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    • pp.325-331
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    • 2013
  • In this study, a complex eigenvalue analysis is implemented to verify the unstable mode of a brake system using ABAQUS software. The component participation factors and component modal participation factors are used to analyze the total contributions from each component and each component mode to a particular unstable system mode. This study shows that the 1.4-kHz unstable system mode comes from mode coupling between the 2nd nodal diametric mode and 3rd lateral axial mode (LAM) in the baseline model. A sensitivity analysis with a linking index is performed to prevent the mode coupling of the component modes. This linking index analysis shows the optimum mass loading position to move away the natural frequency of the 3rd LAM, which contributes to the unstable mode. Finally, a complex eigenvalue analysis is implemented with mass loading in the tie bar position, and no unstable system mode is generated in the low-frequency range (below 2 kHz).

Vibration Characteristics of Steam Generator U-tubes with Defect (결함을 가진 증기발생기 U-튜브의 진동특성)

  • 조종철;정명조;김웅식;김효정;김태형
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.13 no.5
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    • pp.400-408
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    • 2003
  • This paper investigates the vibration characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio. Also, addressed is the effect of the internal pressure on the vibration characteristics of the tube.

Instability of the output intensity of Nd:YAG ring laser with the frequency detuning (고리형 Nd:YAG 레이저에서 진동수 어긋남에 의한 출력세기의 불안정성)

  • 박대윤;김기식;이재철;길상근;홍정미
    • Korean Journal of Optics and Photonics
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    • v.8 no.3
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    • pp.204-208
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    • 1997
  • We analyze the intensity characteristics of the output beams of the ring laser, in which only one mode is generated in each direction, within the neoclassical model by using the Maxwell-Bloch equation. Considering the Nd:YAG crystal as a gain medium, we investigate the stability and the modulation of the output beam intensity as the pumping rate, the relaxation or the decay rate, and the frequency detuning vary, upon taking into account the effect of the beam in one beam in one direction onto the beam in the other direction. In particular, we examine the variation of the output beam intensity and the stability condition through a computer simulation.

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Linear stability analysis in a solid-propellant rocket motor (고체추진 로켓모터에서의 선형 안정성 해석)

  • ;;Kim, Kyung-Moo;Yoon, Jae-Kun
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.10
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    • pp.2637-2646
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    • 1995
  • Combustion instability in solid-propellant rocket motors depends on the balance between acoustic energy gains and losses of the system. The objective of this paper is to demonstrate the capability of the program which predicts the standard longitudinal stability using acoustic modes based on linear stability analysis and T-burner test results of propellants. Commercial ANSYS 5.0A program can be used to calculate the acoustic characteristic of a rocket motor. The linear stability prediction was compared with the static firing test results of rocket motors.