• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.35.3-36
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• 2016

Density and velocity perturbations in scales most relevant for the first galaxy formation are strongly affected by large-scale density perturbations, velocity-divergence perturbations and the baryon-cold dark matter (CDM) streaming velocities. Even at redshifts as high as z~200, this mode-mode coupling imprints a significant impact on the small-scale perturbations, at the wavenumber k >${\sim}100Mpc^{-1}$, as was calculated in our recent work. This implies that cosmological initial conditions based on the usual linear theory is no longer valid in these scales. We present a new cosmological initial condition generator, BCCOMICS, which generates initial conditions for the cold dark matter (CDM) and baryons in scales most relevant for the first galaxy formation. BCCOMICS is based on the linear perturbation theory including the mode-mode coupling terms, and generates cosmological initial conditions for the SPH-basded code GADGET and the AMR-based code ENZO. We also present our preliminary result on the cosmic variance of the first galaxy formation, studied by using BCCOMICS.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.908-912
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• 2003

비대칭 마그네트론 스퍼터링법을 사용하여 실리콘 기판위에 hydrogenated amorphous carbon (a-C:H) 박막을 성장시켰다. DC Power 와 $Ar/C_2H_2$ 의 분압을 변화시켜 증착조건을 형성하고 성장된 다이아몬드상 카본박막의 물성을 관찰하였다. DC 전압에 따라 증착율과 표면 거칠기는 감소하는 한편 박막의 경도는 증가한다. 또한 $Ar/C_2H_2$의 분압이 낮을 때 박막의 특성을 보여주는 G 피크가 낮은 wavenumber로 이동하는 것을 알 수 있다.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.39-41
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• 2003

n this paper, direct numerical simulation of decaying compressible turbulence with passive scalar is performed by using 7th order upwind difference scheme or 8th order group velocity control scheme. The start Reynolds number (defined by Taylor scale) is 72 and turbulent Mach numbers are 0.2-0.9. The Schmidt numbers of passive scalar are 2-10. The Batchelor k-1 range are found in scalar spectra, and the high wavenumber spectra decays faster with increasing turbulent Mach number. The extend self-similarity (ESS) is found in the passive scalar in compressible turbulence.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.779-782
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• 2002

We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.110-113
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• 2005

Theoretical models to study the vibro-acoustic performance of a sandwich panel are proposed. The wave propagation characteristics are analyzed, and dispersion relation is derived. The vibration Is analyzed using the Mindlin plate theory. The vibration of the compliantly supported Mindlin plate is investigated using the Rayleigh-Ritz method. The Timoshenko beam functions are used as trial functions. The model is applied to numerically investigate the influence of the plate mechanical properties. The vibro-acoustic properties are mostly determined by bending deformation at low frequencies. At higher frequencies, the shear deformation has a strong influence. The proposed numerical model is used to estimate the optimal panel properties that result in minimum sound radiation. With increasing dynamic stiffnesses the vibration response decreases but the radiating wavenumber components increase.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.75-82
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• 2001

A dynamic interaction analysis of an adjacent surface fecundation on a layered half-space is performed in the frequency domain. A semi-analytical approach is employed to reduce the integration range of the wavenumber in the surface fundamental solution for a layered half-space in boundary element (BE) formulations. The present study then adopts a combined boundary and finite element method to analyze the dynamic behavior of a system of flexible surface foundations on an elastic homogeneous and layered half-space. Numerical examples are presented to demonstrate the accuracy of the developed method. The examples show the feasibility of an extended application fur the complicated dynamic interaction of foundations on layered media.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.232-240
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• 2013

This paper presents recent advances in damage visualization algorithms of laser generated ultrasonic propagation imaging(UPI) system. An effective damage evaluation method is required to extract correct information from raw data to properly characterize anomalies present in structure. A temporal-reference free imaging system provides easy and rapid defect inspection capability with less computational complexity. In this paper a number of methods such as ultrasonic wave propagation imaging(UWPI), anomalous wave propagation imaging(AWPI), ultrasonic spectral imaging(USI), wavelet ultrasonic propagation imaging(WUPI), variable time window amplitude mapping(VTWAM), time point adjustment(TPA), time of flight and amplitude mapping(ToF&Amp) and ultrasonic wavenumber imaging(UWI) are discussed with instances of successful implementation on various structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1667-1674
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• 2000

A new method is proposed to measure the flow rate in a pipe by multiple measurements of acoustic pressure using a microphone array. It is based on the realization that variation in flow velocity affects the change in wave number. The method minimizes measurement random errors and sensor mismatch errors thereby providing practically realizable flow rate measurement. One of the advantages of the method is that it does not obstruct the flow field and can provide the time-spatial mean flow rate. Numerical simulations and experiments were conducted to verify the utility of this method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.804-810
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• 2000

In this paper, an experimental identification method is presented to identify the bulge wave and extensional wave propagation speeds in the fluid-filled elastic hose. An fluid-filled hose is hanged vertically for straight position. The exciting device of piston type is developed to generate the bulge wave and extensional wave in the elastic hose. Hydrophones are arranged in the fluid-filled hose linearly to measure the wave pressure. The wave speeds are estimated using the wavenumber-frequency spectrum analysis technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.817-824
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• 2000

It is essential to analyze structural vibrations due to turbulent wall pressure fluctuations over a body surface which moves through a fluid, because the vibrations can be a severe source of noise affecting to passengers in airplanes and SONAR performance. Generally, this kind of problems have been solved for very simplified models, e.g. plates, which can be applied to the wavenumber domain analysis. In this paper, a finite element modeling of the wall pressure fluctuations over arbitrary smooth surfaces is investigated. It is found that the modeled wall pressure fluctuation at nodes becomes uncorrelated at higher frequencies and at lower flow speeds, and the response is over-estimated due to the aliased power. Finally, the frequency range available for uncorrelated loading model and two power correction schemes are presented.