• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.433-436
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• 2005

착화기 및 Can 형태의 점화기를 대기압 이하의 압력에서 사용할 때 나타나는 연소현상과 이에 따른 문제점에 대해서 연구를 수행하였다. 착화기 및 점화기가 일정 수준 이상의 진공도에서 작동할 때 최초 연소화염이 정상적으로 연소하지 못할 수 있으며, 경우에 따라서 점화에 완전히 실패할 가능성도 있는 것으로 나타났다. 이러한 현상은 점화된 상태로 분출된 점화제가 자유체적(free volume)내의 낮은 압력에 노출되면서 화약의 연소성이 급격히 떨어져서 나타난 것으로 점화기 내에서 연소상태로 분출된 가스가 자유체적 내에서 초기에 가능한 높은 압력을 형성하도록 하여 개선할 수 있음이 확인되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.187-193
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• 2007

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}\;-\;{\omega}$ turbulence model. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 for two-dimensional case, same aspect ratios with the W/D ratio of 2 for three-dimensional case. The Mach and Reynolds numbers are 0.53 and 1,600,000 respectively. The flow field is observed to oscillate in the "shear layer mode" with a feedback mechanism. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formula. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster.

• 에너지공학
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• 제5권1호
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• pp.80-86
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• 1996

석탄액화반응의 모델반응으로 나프탈렌의 수소화반응을 소형반응기내에서 수행하였다. 생성물인 테트랄린 및 데칼린의 몰분율은 반응온도와 수소압력에 민감하였다. 38$0^{\circ}C$에서 입자촉매를 사용한 반응은 재현성이 낮았으며 이의 규명을 위한 다양한 방법이 시도되었다. H$_2$S에 의한 효과가 가장 관련이 깊은 것으로 추론되었으며 25$0^{\circ}C$에서 H$_2$S의 효과를 체계적으로 규명하였다. H$_2$S의 분압을 조절하여 중간유도체인 테트랄린의 분율을 최대화할 수 있었으며 반응온도 및 반응시간과 함께 H$_2$S의 분압이 황화촉매를 사용하는 석탄액화반응에서 중요한 실험인자임을 확인하였다.

• 한국작물학회지
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• 제44권1호
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• pp.55-58
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• 1999

Plant water status during growth is directly and indirectly associated with seed yield. The objective of the present study was to determine the genotypic differences in leaf water characteristics at an early growth stage of soybean [Glycine max (L.) Merrill] plants through the pressure-bomb technique. Measurements of water potential as well as relative water content (RWC) were made at the third leaf from the fully-expanded top leaf of eight different soybean genotypes grown for 31 to 35 days after field emergence. On the basis of the modified exponential model, pressure-volume (PV) curves were fitted well ($R^2$=0.92＊＊ to 0.99＊＊ for the curvi-linear region and R=0.67＊＊ to 0.96＊＊ for the linear region), indicating that a segmented model using PROC NLIN of SAS could be used effectively to estimate the leaf water characteristics. The regression analysis for the pressure-volume (PV) curve revealed genotypic variation in the solute potential at saturation (Ψ$_{s,sat}$ :-10.7 to -14.8 bar), solute potential at incipient plasmolysis (Ψ$_{s,ip}$ : -14.3 to -18.3 bar), RWC at incipient plasmolysis (RW $C_{ip}$ : 83.3 to 91.7%), high integrated turgor pressure from saturation to plasmolysis ( $_1$$^{b}$ : 0.39 to 0.81), and maximum volumetric modulus of elasticity ($\varepsilon$$_{max}$ : 150 to 445 bar).).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• 한국자동차공학회논문집
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• 제18권6호
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• pp.53-62
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• 2010

An airbag is composed of housing assembly, door assembly, cushion assembly, and an inflator. The inflator is the essential part that generates gas for airbag. When an airbag is activated, it effectively absorbs the crash energy of the passenger by inflating a cushion. In this study, tank tests were performed with newly synthesized propellants with various compositions, and the results are compared with the numerical results. In the simulation of inflator, a zonal model has been adopted which consisted of four zones of flow regions: combustion chamber, filter, gas plenum, and discharge tank. Each zone was described by the conservation equations with specified constitutive relations for gas. The pressure and temperature of each zone of the inflator were calculated and analyzed and the results were compared with the tank test data. In the zone of discharge tank the pressure quickly rose, the pattern of pressure curve was very similar to the pressure curve of real test. And in zone 1 & 2 & 3 the mass of products was increased and decreased with time. In zone 4, the mass of products was increased with time like real inflator. From the similarity of pressure curve in zone 4 and closed bomb calculation the modeled results are well correlated with the experimental values.

• 대한기계학회논문집
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• 제16권3호
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• pp.589-597
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• 1992

본 연구에서는 고압하의 분무연소에 있어서 매연생성에 대한 기초적 자료를 얻기 위해 난류 확산화염의 복잡한 디이젤 분무연소를 예혼합기에 의한 단순한 연소에 서 모델링 될 수 있는 특수 정적연소 장치를 제작했다. 이러한 정적 연소용기내의 프로판-공기 예혼합기연소를 대상으로, 주로 압력이 매연생성에 미치는 영향을 2색법 에 의한 연소가스온도측정과 더불어 4MPa까지의 넓은 압력범위에 걸쳐 조사했다.

• 한국추진공학회지
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• 제22권2호
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• pp.66-73
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• 2018

밀폐용기 내 Zirconium/Potassium Perchlorate의 연소를 수치적 모델링을 통해 전산해석을 수행하였다. 5차 WENO 공간차분법과 improved delayed detached eddy (IDDES) 난류모델을 사용하여 충격파가 동반되는 내부 유동구조를 모사하였고, 라그랑지안 연소모델을 통해 화약 입자를 계산하였다. 옆면 중앙에 센서가 설치된 원통형 밀폐용기 내부 유동분석을 통해 압력 진동이 발생하는 원인을 규명하였다. 또한 센서 다이어프램 깊이 변화에 따라 측정되는 압력 데이터를 실험값과 비교분석 하였다. 그 결과 센서 탭의 깊이가 약 2.36 mm 이상으로 커지면 유동속도가 아음속으로 감쇠하고 복잡한 eddy가 발생하여 측정값에 큰 불규칙성을 야기하는 현상을 관측하였다.

• 한국전산유체공학회지
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• 제13권1호
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• pp.35-40
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• 2008

Generally flight vehicles have many cavities such as wheel wells, bomb bays and windows on their external surfaces and the flow around these cavities makes separation, vortex, shock and expansion waves, reattachment and other complex flow phenomenon. The flow around the cavity makes abnormal and three-dimensional noise and vibration even thought the aspect ratio (L/D) is small. The cavity giving large effects to the flow might make large noise, cause structural damage or breakage, harm the aerodynamic performance and stability, or damage the sensitive devices. In this study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa-\omega$ turbulence model. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 with the W/D ratio of 2 for three-dimensional cavities. The Sound Pressure Level (SPL) analysis was done with FFT to check the dominant frequency of the cavity flow. The dominant frequencies were analyzed and compared with the results of Rossiter's formula and Ahuja& Mendoza's experimental datum.

• 한국군사과학기술학회지
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• 제8권4호
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• pp.146-151
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• 2005

The burning rates of combustible cartridge cases(CCCs) of 120mm kinetic energy ammunition were measured by CBT(Closed Bomb Tester). The burning coefficient was 1.4 for CCC fabricated by Post Impregnation(PI) process, and 1.0 for that by Beater Additive(BA) process. The BA process CCC showed the fixed burning coefficient of 1.0 in spite of changing the composition of CCC. As the Korean Future Main Battle Tank is requiring the high penetration performance compared with that of KlAl tank ammunition(K276), CCC was designed to have higher impetus composition than that of K276 composition(525J/g). The optimum impetus was 600J/g when considering the increases of pressure and muzzle velocity with increasing impetus. When impetus of CCC by changing the composition increased from 525J/g to 600J/g, the muzzle velocity of 12m/s at pressure increase of 3500psi increased in case of using SCDB propellant.