• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.94-97
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• 2003

The effect of pressure perturbation in the ramjet engine on the characteristics of the inlet is studied via numerical simulation. The frequency and amplitude of the pressure perturbation are assumed to be 500Hz and 20% of the exit back pressure, respectively. The simulation shows the characteristics of the normal shock in the inlet according to the pressure perturbations. The relation between the captured mass flow rate and downstream pressure perturbation is studied. The mass flow rate decreases when the downstream pressure perturbation starts.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.3
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• pp.209-218
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• 1995

Nonlinear interaction between directional wave components is theoretically analyzed in deep water. The perturbed solution for an irregular wave is derived accurate up to the third order of the wave steepness and it is shown that the wave characteristics are modulated due to the nonlinear interaction. The convergence rate of the perturbed solution depends on not only wave steepness but also wavelength ratio between wave components. The long-wave component of the perturbed solution converges rapidly. while the short-wave solution converges slowly or diverges. The short wave properties in a broad-band wave spectrum cannot accurately be obtained by the conventional wave-mode method because it fails to properly describe the modulation of short-wave frequency caused by the nonlinear interaction with much longer wave.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.415-418
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• 2011

It is critical to assess the characteristics of flame response to pressure perturbations for the understanding of nonlinear combustion instabilities. Previous studies can be grouped into flame response upon perturbed, fresh air and fuel mixture, and flame response directly perturbed from longitudinal waves. The present study presents experimental methodology for the understanding of the flame response exposed to transverse acoustic waves generated by loud speakers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.79-87
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• 2002

Acoustic responses to pressure oscillations in axisymmetric combustion chamber are numerically investigated to examine the qualitative trend of acoustic instability in liquid rocket engine. Chamber operating condition and excitation frequency of oscillating pressure are selected as exciting parameters of acoustic instability. Artificial perturbation is simulated by total-pressure oscillation with sine wave at chamber inlet. Many approximations and simplifications are introduced without losing the essence of acoustic pressure response. First, steady-state solution for each operating condition is obtained and next, transient analysis is conducted. Depending on operating condition and excitation frequency, the distinct response characteristics are brought. Weak-strength flames and high-frequency excitation tend to cause sensitive acoustic pressure response leading to unstable pressure field. These results are analyzed based on the correlation with acoustic pressure responses from the previous works adopting laminar flamelet model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.295-298
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• 2008

In this paper, prototype dynamic modeling scheme to control ramjet propulsion systems were proposed. From the physical understandings of engine system, a typical 2nd-order system model was applied to simulate the dynamic characteristics of fuel supply system. The shock location varience in diffuser to chamber pressure fluctuation is calculated so that the out of phase between two signals was observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.718-723
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• 2017

In this paper, Analytical study is carried out on the impedance characteristics of the globe control valve, which is mainly used for thrust control in liquid rockets, according to the effective area at low frequency perturbation. The impedance tends to increase according to effective area and the cause of impedance characteristic change through flow field visualization is investigated. In the future, the information on the change in the impedance characteristics of the control valve can be used to obtain the impedance of the supply system and it can be utilized to predict pogo phenomenon as well as design accumulator and orifice to reduce the pogo phenomenon.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.5
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• pp.8-14
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• 2010

For the development of a liquid rocket engine, hot-firing tests of a regeneratively cooled thrust chamber were performed at chamber pressures of approximately 30 and 60 bars. In the paper, pressure fluctuation data, which were obtained from the dynamic pressure transducers installed in propellant manifolds and combustion chamber, were analyzed. Compared to the data at chamber pressure of 60 bar, the results at chamber pressure of 30 bar showed low-frequency oscillations around 150 Hz in the combustion chamber. The low-frequency waves in the combustion chamber were coupled with those in the manifolds. However, the RMS values of the chamber pressure fluctuations at chamber pressure of 30 bar were only 0.8% of the chamber pressures. Thus, it can be inferred that the thrust chamber operates in the stability boundary even at low chamber pressure.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.72-75
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• 2005

The profiles of the second-order higher harmonics during B-H hysteresis loop have been measured as functions of the tensile stress in grain-oriented $3.2{\%}$ Si steels. The observed harmonics profiles have been analyzed in terms of the nonlinear, asymmetric magnetization which reflects the domain reorientation under the field. The field interval of the second-order higher harmonics is related to the nucleation and annihilation fields and a measurement method for the magnetostriction is proposed using the harmonics profiles under tensile stress.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.2
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• pp.19-28
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• 2010

Generally, combustion instability is generated by the mutual coupling between the heat release and the acoustic pressure in the combustor. On the occasion, the acoustic pressure generates the oscillation of the mass flow rate of propellant injected from injector, and this oscillation again affects combustion in the combustor. So, the dynamic characteristics of the injector have been studied to control combustion instability using injector itself in Russia from 1970's. In order to study injector dynamics, a mechanical pulsator for forced pressure pulsation is produced and the method to quantify the mass flow rate of the propellant that is oscillating at the exit of the injector is developed. With the pulsator and the method, pulsating values of the mass flow rate, pressure, liquid film thickness, and axial velocity generated at the exit of the simplex swirl injector are measured in real time. And phase-amplitude characteristics of each parameter are analyzed using these pulsating values acquired at the exit of the simplex swirl injector.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.35-40
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• 2011

An experimental study of the flame response in a turbulent premixed combustor has been conducted in order to investigate mechanisms for combustion instabilities in a lean premixed gas turbine combustor. A lab-scale combustor and mixing section system were fabricated to measure the flame transfer function. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results show that the flame transfer functions are greatly dependent on the modulation frequency as well as operating conditions such as equivalence ratio. Flame dynamics can be generalized as a function of Strouhal number which is a ratio of flame length to modulation wave length.