• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.622-627
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• 2017

In this study, the numerical analysis of propellant supply manifold of a sub-scale model combustor with the same combustion and acoustic resonance conditions as the real combustor was carried out. The analysis of the results is based on the shape of the manifold and the number and type of inflow channels. The manifold form of the main propellant was rounded so that the recirculation area was small and easy to manufacture. The liquid oxygen mainfold included a distributor to uniformly supply the flow, and since the kerosene manifold was directly in contact with the flame side, the inflow channel was formed at a radial $360^{\circ}$ so as to minimize the recirculation region. The liquid nitrogen manifold was configured as a radial inflow channel to reduce the velocity difference near the injector.

• Journal of computational fluids engineering
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• 제6권4호
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• pp.26-34
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• 2001

The flow past a circular cylinder forced to vibrate transversely is numerically simulated by solving the two-dimensional Navier-Stokes equations modified by the vibration velocity of a circular cylinder at a Reynolds number of 164. The higher-order finite difference scheme is employed for the spatial discretization along with the second order Adams-Bashforth and the first order backward-Euler time integration. The calculated cylinder vibration frequency is between 0.60 and 1.30 times of the natural vortex-shedding frequency. The calculated oscillation amplitude extends to 25% of the cylinder diameter and in the case of the lock-in region it is 60%. It is made clear that the cylinder oscillation has influence on the wake pattern, the time histories of the drag and lift forces, power spectral density and phase diagrams, etc. It is found that these results include both the periodic (lock-in) and the quasi-periodic (non-lock-in) state. The vortex shedding frequency equals the driving frequency in the lock-in region but is independent in the non-lock-in region. The mean drag and the maximum lift coefficient increase with the increase of the forcing amplitude in the lock-in state. The lock-in boundaries are also established from the present direct numerical simulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.873-876
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• 2011

In this research, a Helmholtz resonator was applied to the thermo-acoustic environment that has thermal gradient using Rijke tube. The thermo-acoustic instability was invoked by a Rijke tube which use a DC power supplier and a Blower. A target instability frequency was appeared by the Rijke tube. A preliminary experiment on damping characteristics of the resonator in the thermo-acoustic environment was performed and compared with the room temperature experiment data.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제26권4호
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• pp.515-523
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• 2002

Effects of rotary oscillation on unsteady laminar flow past a circular cylinder have been investigated in this study. Numerical simulations are performed for the flow at Re=100 in the range of 0.2<$\Omega$<2.5 and 0.02<$St_f$<0.8, where $\Omega$ and $St_f$ are, respectively, the maximum rotation velocity and rotation frequency normalized by the free-stream velocity and cylinder diameter. Results show that rotary oscillation has significant effects on the flow. When the rotation frequency is near the natural vortex-shedding frequency, lock-on occurs and the lock-on frequency range becomes wider as the rotation velocity increases. In a certain range of the rotation frequency and velocity, modulations in the velocity, lift and drag signals occur and this modulation frequency is expressed as a linear combination of the rotation frequency and vortex-shedding frequency. The mean drag and amplitude of the lift fluctuations show local minima near the boundary between the lock-on non and lock-on regions.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제25권3호
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• pp.182-188
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• 2016

This study investigates cavity flows through a guide grill above a resonator. Vortex distributions and intake flows are simulated for various shapes of the guide grill. The flows are assumed to be compressible, unsteady, and turbulent. Numerical simulations are conducted using a large eddy simulation (LES) model. To analyze the effect of the guide grill shape, three cavity lengths (0.2H, 0.6H, and 1.0H) and cavity angles ($30^{\circ}$, $45^{\circ}$ and $60^{\circ}$) are considered based on resonator height (H). The results show that the vortex generated in the resonator by cavity flow increases with cavity length. Thus, the intake flow is minimum at the smallest cavity length and angle. However, when cavity length is equal to resonator height, the intake flow decreases. The maximum intake flow occurs at a cavity angle $45^{\circ}$ at higher cavity lengths owing to the interaction between the vortex in the resonator and intake flow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.648-654
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• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• Journal of the Korean Society of Propulsion Engineers
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• 제21권4호
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• pp.63-70
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• 2017

ZPP (Zirconium-Potassium Perchlorate) is type of primary charge initiators for PMD (Pyrotechnic Mechanical Device) system. The binder component dissolved in the solvent is precipitated to suspended particles in the granules. The LabRAM Mixer uses resonance phenomenon to transfer energy, unlike blade equipment that utilizes mechanical contact. In this study, the properties of the particles prepared by the LabRAM Mixer were evaluated with the changes of the conditions.

• Journal of the Society of Naval Architects of Korea
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• 제29권1호
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• pp.55-60
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• 1992

A study has been made on the hydrodynamic forces on and the motion response of a sliding block in a bay within the framework of linear potential theory. To simplify the problem, following assumptions are made : The configuration of the bay is a long channel with narrow width, constant depth and straight coastline. Incident waves are long compared to the depth. We applied matched asymptotic expansion techniques. The flued domain is subdivided into three regions ; ocean, bay entrance, bay regions. Boundary-vague problems are solved first in each region. Then unknown coefficients are determined by matching individual solutions at the intermediate region between two neighboring legions. It is found that the motion of the block is greatly amplified at the resonant frequencies, in particular at the quarter wavelength mode. We examined the mechanism of negative added mass, which results from the localized hydrodynamic resonance.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.466-474
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• 2008

The purpose of this study was to comparatively analyze the measured values and modelling values when a sample mountain was cut and thereby, assess the fitness of the prediction model. For this purpose, the researcher analyzed the relationship between the groundwater levels measured at 7 monitoring holes set within the area of the underground flow prediction model and the levels of the groundwater monitoring holes before and after mountain cutting. As a result of this analysis, it was found that the MODFLOW program itself was limited and uncertain in terms of calibration of the modelling values. Since the model was based on the assumption that the same amount of rainfalls would permeate into the ground when the sample mountain area was cut up to 50m high, it was deemed inevitable that the result of modelling was different from the actual measurement.

• Proceedings of the KIPE Conference
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.429-430
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• 2013

대용량 계통연계형 인버터에서 필터의 사이즈와 가격을 줄이고, 빠른 동적 특성을 얻기 위해서 LCL필터가 많이 사용된다. LCL필터 설계 시에 계통으로 유입되는 고조파 전류를 제한하는 것이 주된 목적이지만, LCL필터가 가지는 공진 특성 또한 고려되어야 한다. 그리고 인버터 전류 피드백으로 전류 제어 루프를 구성하는 경우와는 달리 계통 전류 피드백으로 인버터의 전류 제어 루프를 구성하게 되면 전자보다 더 안정적인 운전영역을 확보하게 된다. 하지만 이러한 운전영역 또한 LCL필터를 어떻게 설계하느냐에 따라 달라진다. 본 논문에서는 계통전류의 고조파 제한과 함께 전류제어기의 안정성을 고려한 LCL필터 설계 기법을 제안하고자 한다. 제안된 설계 기법을 통해서 얻어진 결과를 7.5kW급 계통연계형 인버터 시작품을 통해서 검증하였다.