• 한국전산유체공학회지
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• 제17권4호
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• pp.69-74
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• 2012

Hypersonic flowfields over a sphere is calculated by using a nonequilibrium flow solver. The flow solver features a two-temperature model and finite rate chemical reaction models to describe nonequilibrium thermochemical processes. For the purpose of validation, the calculated shock stand-off distance is compared with the experimental data which is measured in a ballistic range facility. The present nonequilibrium calculation well reproduced the experimental shock stand-off distance in the cases where the experimental flowfields are expected to be nearly equilibrium, as well as in the cases to be nonequilibrium flowfields in the velocity range 4000 to 5500 m/s.

• 천문학회보
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• 제41권1호
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• pp.81.3-81.3
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• 2016

We examine whether the observational stand-off distance ratios of CMEs and their associated ICMEs could be explained by theoretical model or not. For this, we select 16 CME-ICME pairs from September 2009 to October 2012 with the following conditions: (1) limb CMEs by SOHO and their associated ICMEs by twin STEREO spacecraft and vice versa when both spacecraft were roughly in quadrature; (2) the faint structure ahead of a limb CME is well identified; and (3) its associated ICME clearly has a sheath structure. We determine the observational stand-off distance ratios of the CMEs by using brightness profiles from LASCO-C2 (or SECCHI-COR2) observations and those of the ICMEs by solar wind data from STEREO-IMPACT/PLASTIC (or OMNI database) observations. We also determine the theoretical stand-off distance ratios of the CME-ICME pairs using semi-empirical relationship based on the bow shock theory. We find the following results. (1) Observational CME stand-off distance ratio decreases with increasing Mach number at the Mach numbers between 2 and 6. This tendency is consistent with the results from the semi-empirical relationship. (2) The observational stand-off distance ratios of several ICMEs can be explained by the relationship.

• 한국전산유체공학회지
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• 제19권1호
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• pp.7-14
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• 2014

Aerothermodynamic characteristics of re-entry vehicles in hypersonic speed regimes are investigated by applying CFD methods based on the Navier-Stokes-Fourier equations. A special emphasis is placed on the effects of high temperature chemically reacting gases on shock stand-off distance and thermal characteristics of the flowfields. A ten species model is used for describing the kinetic mechanism for high temperature air. In particular, the hypersonic flows around a cylinder are computed with and without chemically reacting effects. It is shown that, when the chemically reacting effects are taken into account, the shock stand-off distance and temperature are significantly reduced.

• 한국연소학회지
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• 제1권2호
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• pp.41-49
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• 1996

A numerical study is conducted to investigate the periodically unstable shock induced combustion around blunt bodies in stoichiometric hydrogen-air mixtures. Euler equations are spatially discretized by upwind-biased third order scheme and temporally integrated by Runge-Kutta method. Chemistry model used in this study involves 8 elementary kinetics steps and 7 species. At a constant Mach number, the effects of projectile size, inflow pressure and inflow temperature are examined with Lehr#s experimental condition as a reference. In addition to oscillation frequency, characteristic distances and time averaged values are found from the result to find an relation with dimensionless parameters. As a result, it is found that the effects of inflow pressure and body size are very similar and $Damk{\ddot{o}}hler$ number plays an important role in determining the instability characteristics.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.425-435
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• 2017

In this work, an overview of flow diagnosis in a shock tunnel is made by means of using established techniques that are easy to setup, economical to arrange, and simple to measure. One flow condition was considered having Mach number of 6 at the nozzle-exit, regarded as freestream. Measured aerothermodynamic data such as shock wave speed, wall static and total pressures, surface heat flux, and shock stand-off distance ahead of test model showed good agreement with calculation. This study shows an overall procedure of flow diagnosis in a shock tunnel in a single manuscript. Outcomes are thought to be useful in the field of education and also in a preliminary stage of high-speed vehicle design and tests, that need to be performed within a short time with decent accuracy.

• 한국해양공학회지
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• 제36권3호
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• pp.161-167
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• 2022

Three-dimensional finite element analysis (3D-FEA) models have been used to evaluate the shock-resistance responses of various equipments, including armaments mounted on a warship caused by underwater explosion (UNDEX). This paper aims to check the possibility of using one-dimensional (1D) FEA models for the shock-resistance responses. A frigate was chosen for the evaluation of the shock-resistance responses by the UNDEX. The frigate was divided into the thirteen discrete segments along the length of the ship. The 1D Timoshenko beam elements were used to model the frigate. The explosive charge mass and the stand-off distance were determined based on the ship length and the keel shock factor (KSF), respectively. The UNDEX pressure fields were generated using the Geers-Hunter doubly asymptotic model. The pseudo-velocity shock response spectrum (PVSS) for the 1D-FEA model (1D-PVSS) was calculated using the acceleration history at a concerned equipment position where the digital recursive filtering algorithm was used. The 1D-PVSS was compared with the 3D-PVSS that was taken from a reference, and a relatively good agreement was found. In addition, the 1D-PVSS was compared with the design criteria specified by the German Federal Armed forces, which is called the BV043. The 1D-PVSS was proven to be relatively reasonable, reducing the computing cost dramatically.

• 대한기계학회논문집
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• 제16권6호
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• pp.1108-1114
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• 1992

본 연구에서는 폭발용접 성능평가에 중요한 영향을 주고 있는 기폭방법을 비 교하고, 선형 충격파의 발생방법과 이에 의한 접합 결과를 실험적으로 나타내고자 한 다.

• 한국항공우주학회지
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• 제45권11호
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• pp.914-921
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• 2017

우주발사체 고공환경모사의 실험적 연구는 우주발사체 발사 및 임무완수에 대한 독자적 기술력 확보를 위해 중요하다. 본 연구는 한국형발사체(Korean Space Launch Vehicle; KSLV-II)의 발사 후 마하수 6을 돌파하는 고도 65 km 조건을 선정하였다. 지상시험장비중 하나인 충격파 터널을 이용하여 고공환경모사를 수행하였다. 유동발달 이후 공기열역학적 특성과 수직 및 경사충격파 확인을 위해 선두부 모델의 정체 압력과 정체 열 유량, 그리고 반구형상 모델의 충격파 이탈거리 측정을 통해 유동검증을 수행하였다. 추가적으로 발사체 측면과 저부면 현상연구에 사용되는 시험모델의 자유류 회복을 위한 충격파 상쇄 기법을 개발 및 검증하였다. 세 가지 유동검증 결과를 통해 이론값과 약 ${\pm}3%$ 이내의 오차를 갖는 정확한 유동이 발달되었음을 확인하였다. 그리고 충격파 상쇄기법을 갖는 천이구간 축소 모델의 경사충격파 경사각과 수평 평판모델의 경사각, 그리고 모델 측면 정압력의 실험값과 이론값의 오차가 각각 2%, 그리고 1% 으로 확인되었으며, 이를 통해 해당 충격파 상쇄 기법의 합리적인 효과가 검증되었다.