• 한국안전학회지
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• 제26권2호
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• pp.32-35
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• 2011

다중 장애물을 가지는 폭발챔버에서 전파하는 화염과 국부 장애물의 상관관계를 조사하기 위하여 실험적 연구를 수행하였다. 폭발챔버 높이 235 mm, 단면적 $1,000{\times}950\;mm^2$, 벤트면적 $1,000{\times}320\;mm^2$를 가지는 폭발챔버를 제작하였으며, 30% blockage ratio를 가지는 장애물을 챔버내에 설치하였다. 전파하는 화염과 장애물의 상관관계를 조사하기 위해 고속카메리를 사용하였다. 고속카메라로 얻어진 화염 이미지로부터 장애물 주위의 국부 화염전파 거동은 2가지 다른 방법, 즉 전파하는 화염전면(flame front)의 각 pixel point에서 산정된 평균 화염전파속도와 연소면적 증가(incremental burnt area)/화염전면 길이(flame front length) 관점에서 분석하였다. 분석결과, 2가지 방법으로 얻은 결과는 거의 일치하는 경향을 나타났으며, 전파하는 화염이 장애물의 전면과 상호 작용할 때 화염속도는 급격히 증가하다가 장애물의 후단면에서 약간 감소하고, 화염이 장애물 후단에서 재결합될 때 다시 급격히 증가하였다.

• 한국재료학회지
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• 제11권3호
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• pp.164-170
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• 2001

자전고온합성반응법을 이용하여 이규화 몰리브덴-텅스텐($Mo_{1-z}$ , $W_{z}$)$Si_2$을 합성하였다. 조성 (z)을 변화시켜 성형한 원통형 시편에 합성반응 중 전달되는 온도변화를 예측하기 위하여 시편의 중앙에 열전대를 삽입하였다. 반응 선단면이 열전대를 통과할 때 가장 높은 반응온도를 보이고 이것을 단열반응 온도라 간주하였다. 따라서 본 연구에서는 이러한 온도변화를 예측하기 위하여 자전조온합성반응의 모델링을 계시하고자 하였으며, 실험을 통하여 측정한 반응온도 분포곡선의 거동을 비교하였다. 각각의 시료에 대한 실험결과 측정된 반응속도는 약 2.14~1.35mm/sec, 반응온도는 1883K~1507K의 간을 보였다. 두 항 모두 텅스텐의 함량이 증가함에 따라 감소하는 경향을 나타냈으며, 수치해석을 통하여 거의 유사한 반응온도를 얻었다. 시료의 초기온도를 증가시킬 경우 반응온도는 증가함이 예측되었고, z=0.5인 시료에 대하여 반응온도가 1900k 이상이 되기 위해서는 약 800K-900K의 예열이 필요하였다.

• 한국분말재료학회지
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• 제20권5호
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• pp.332-337
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• 2013

Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.

• Composites Research
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• 제18권2호
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• pp.46-51
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• 2005

본 논문은 램파(Lamb waves)를 이용한 능동검사시스템을 구조 건전성 모니터링 시스템에 적용하기 위하여 램파의 특성연구를 수행하였다 연구는 보다 실제 구조물에 근접한 구조물을 고려하여 두께변화가 있는 준등방성 복합재 평판을 대상으로 PZT 탐촉자(transducer)를 표면에 부착하여 수행하였다. 본 연구에서는 두께변화로 인한 램파의 전파특성을 분석하기 위하여 간단하지만 새로운 기법을 적용하였다 본 연구의 결과는 램파의 전파특성은 상대적으로 얇은 구조물에 민감하였고 두께변화가 램파의 전파에 미치는 영향을 보여 주었다. 또한 본 연구에 사용한 분석기법은 램파를 이용한 구조 건전성 모니터링에 적용할 수 있는 가능성을 보여주었다.

• 대한기계학회논문집
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• 제18권10호
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• pp.2686-2697
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• 1994

When a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• 한국자동차공학회논문집
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• 제23권4호
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• pp.402-409
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• 2015

In this study a quasi-dimensional model is developed to predict the combustion process and emissions of a GDI engine under ultra-lean conditions. Combustion of a GDI engine condition is modeled as two simultaneous processes to consider significant fuel stratification. The first process is premixed flame propagation described as burning in a hemispherically propagating flame. The second is diffusion-controlled combustion modeled as mixing of multiple spray zones in the burned gas region. Mixing is an important factor in ultra-lean conditions leaving stratified mixture of developing sprays behind the propagating premixed flame. Sheet breakup and Hiroyasu models are applied to predict the velocity of a hollow cone spray. Validation is performed against measured pressures and NOx and CO emissions at different load and rpm conditions in the test engine.

• 천문학회보
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• 제36권2호
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• pp.83.1-83.1
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• 2011

Solar flares are very spectacular, and are associated with various phenomena. Coronal shocks or disturbances are one of such flare-related phenomena. Although Moreton waves and X-ray waves are well explained with MHD first mode shocks propagating in the corona, there still remains a big problem on the nature of the waves, since they are very rare phenomena. On the other hand, EIT waves (or EUV waves) have been paid attention to as another phenomenon of coronal disturbances. However, the physical features (velocity, opening angle, and so on) are much different from those for Moreton waves and X-ray waves. We report detailed features of the coronal disturbances associated with the 2010 February 7 and the 2010 August 18 flares. For the former flare we analyzed the H-alpha images obtained by SMART at Hida Observatory, Kyoto University, Japan and by a flare telescope at National Astronomical Observatory of Japan, the X-rays images taken by Hinode/XRT, and the EUV images obtained by the both satellites of STEREO, and found the Moreton wave, X-ray wave, and EIT wave, simultaneously. In the latter flare, on the other hand, we observed a very fast EUV wave in EUV images taken by SDO/AIA. The propagating speed is comparable to the MHD first mode wave, while there is no obvious evidence of shocks for this flare. From these results, we discuss the nature of coronal disturbances.

• 한국세라믹학회지
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• 제30권12호
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• pp.1096-1102
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• 1993

Titanium nitride was synthesized by reacting Ti powder with nitrogen gas using SHS method. In this process, the effects of nitrogen pressure, dilution with TiN, or additiion of titanium hydride(TiH1.924) on the conversion of Ti to TiN were investigated. In particular, much effects were given to solve the problem of the conversion drop due to partial melting and subsequent sintering of Ti parciels, by controlling combustion temperature and combustion wave velocity via mixing Ti powder with TiN or/and TiH1.924. For the diluted titanium powders with TiN, the conversion close to 100% was resulted when the nitrogen pressure was over 8atm and with diluent content of 60wt%, and the self-propagating reaction was not sustained when the diluent content was higher than 60wt%. For samples mixed to be 55wt% in Ti component in the mixture of Ti, TiH1.924, and 45% TiN, the conversion was closed to 100% when the amount of titanium hydride added was over 7wt% and the nitrogen pressure was higher than 5atm. The combustion reaction, however, was not sustained when titanium hydride added was more than 10wt%.

• Geomechanics and Engineering
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• 제21권3호
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• pp.227-236
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• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

• 한국세라믹학회지
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• 제32권6호
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• pp.659-668
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• 1995

Zirconium carbide was prepared from the mixture of metal zirconium and carbon powders in argon atmosphere by Self-propagating High-temperature Synthesis (SHS) in order to obtain the best carbon source and dilution contents. The most exellent result was obtained in the case that active carbon was added as a starting material, 20~30 wt% dilution content. From thermal profile analysis an apparent activation energy of 118 KJ/mol was calculated. The maximum heating rate achieved during 15 wt% ZrC reaction by product dilution method was approximately 1.54$\times$105 K/s. Coupling this value with the measured wave velocity of 1.026cm/s yielded a maximum thermal gradient fo $1.5\times$105 K/cm. Using the definition of t* and the measured wave velocity, the effective thermal diffusivity, $\alpha$, was calculated to be 0.62$\times$102 $\textrm{cm}^2$/s.