• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1256-1265
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• 2006

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. 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, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.311-314
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• 2006

The supersonic flow around tandem cavities was investigated by three- dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes(RANS) equation with the $\kappa-\omega$ thrbulence model. 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, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split using van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratio of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two-dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the fire cavity flow cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.235-238
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• 2005

The unsteady supersonic flow over two- and three-Dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k - w turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. Numerical method is upwind TVD scheme based on the flux vector split with the Van Leer limiters, and time accuracy is used explicit 4th stage Runge-Kutta scheme. Cavity flows are Comparison of two- and three-dimensional. The cavity has a L/D ratio of 3 for two-dimensional case. and same L/D and W/D ratio is 1 for three-dimensional case. The Mach and Reynolds numbers are held constant at 1.5 and 450000 respectively. For the three-dimensional case, the flow field is observed to oscillate in the 'shear layer mode' with a feedback mechanism that follow Rossiter's formula. On the other hand, the self-sustained oscillating flow transitions to a 'wake mode' for the two-dimensional simulation, with more violent fluctuations inside the cavity.

• 비파괴검사학회지
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• 제14권3호
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• pp.177-184
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• 1994

본 연구는 X선 비파괴시험법을 활용하여 피사체 내부에 존재하는 기공의 3차원적 형상, 위치 및 크기를 측정하고 검사 조건에 따른 오차를 최소화하는 계산기법을 제시하였다. 제시한 계산기법을 실용화하기 위하여 기공측정전산코드(PEVACA)를 개발하고 다양한 형상의 모의 기공을 적용한 검증시험과 실제 피사체를 검사 후 절단하여 측정비교시험을 통하여 본 계산기법의 신뢰성을 검토하였다. 본 연구를 통하여 개발된 PEVACA는 작도법에 의한 기존의 수작업보다 측정 신뢰도(${\pm}0.5mm$ 이내의 오차 범위)를 항상시켰을 뿐만 아니라 작업시간 단축과 자료전산화에도 크게 기여할 것으로 판단된다.

• Restorative Dentistry and Endodontics
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• 제41권2호
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• pp.83-90
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• 2016

Objectives: This study was evaluated the marginal microleakage of two different adhesive systems before and after aging with two different dye penetration techniques. Materials and Methods: Class V cavities were prepared on the buccal and lingual surfaces of 48 human molars. Clearfil SE Bond and Single Bond (self-etching and etchand-rinse systems, respectively) were applied, each to half of the prepared cavities, which were restored with composite resin. Half of the specimens in each group underwent 10,000 cycles of thermocycling. Microleakage was evaluated using two dimensional (2D) and three dimensional (3D) dye penetration techniques separately for each half of each specimen. Data were analyzed with SPSS 11.5 (SPSS Inc.), using the Kruskal-Wallis and Mann-Whitney U tests (${\alpha}=0.05$). Results: The difference between the 2D and 3D microleakage evaluation techniques was significant at the occlusal margins of Single bond groups (p = 0.002). The differences between 2D and 3D microleakage evaluation techniques were significant at both the occlusal and cervical margins of Clearfil SE Bond groups (p = 0.017 and p = 0.002, respectively). The difference between the 2D and 3D techniques was significant at the occlusal margins of non-aged groups (p = 0.003). The difference between these two techniques was significant at the occlusal margins of the aged groups (p = 0.001). The Mann-Whitney test showed significant differences between the two techniques only at the occlusal margins in all specimens. Conclusions: Under the limitations of the present study, it can be concluded that the 3D technique has the capacity to detect occlusal microleakage more precisely than the 2D technique.

• 한국전산유체공학회지
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• 제10권4호통권31호
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• pp.51-58
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• 2005

The unsteady supersonic flow over two- and three-dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k-$\omega$ turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in the cavity. An explicit 4th order Runge-Kutta scheme and an upwind TVD scheme based on the flux vector split with the van Leer limiters are used for time and space discritizations, respectively. The cavity has a L/D ratio of 3 for two-dimensional case, and same L/D and W/D ratio of I for three-dimensional case. The Mach and Reynolds numbers are 1.5 and 450000 respectively. In the three-dimensional flow, the field is observed to oscillate in the 'shear layer mode' with a feedback mechanism that follows Rossiter's formula. In the two-dimensional simulation, the self-sustained oscillating flow has more violent fluctuation inside the cavity. The primary fluctuating frequencies of two- and three- dimensional flow agree very well with the 2nd mode of Rossiter's frequency. In the three-dimensional flow, the 1st mode of frequency could be seen.

• 지구물리와물리탐사
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• 제11권4호
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• pp.368-372
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• 2008

이 연구는 카르스트 지역에서 발생하는 연약층 또는 지하 석회암 공동의 영상화를 위한 지표 전기비저항 탐사의 유용성을 파악하고자 수행되었다. 연약층 또는 공동은 잠재적인 위험성을 가지고 있으며, 이들은 도로 및 건축물의 붕괴를 야기한다. 따라서 이 연구에서는 이미 지반침하가 있었음이 보고된 바 있는 전남 무안군 영월리에 있는 한 도로를 따라 2-3차원 전기비저항 탐사를 수행하여 지반 침하 현상을 조사하였다. 이 지역의 쌍극자배열 전기비저항 탐사 결과, 풍화된 표토층과 연약층 또는 공동 그리고 기반암이 뚜렷이 구분되어 나타났으며, 또한 여러 곳의 저비저항 이상대가 나타났는데 이는 점토로 충전된 공동으로 시추결과 확인되었다. 아울러 시추 결과와 전기비저항 탐사 결과는 매우 일치함을 알 수 있었다. 따라서 지반 침하를 평가하는 데 있어 전기비저항 탐사를 통한 지하영상화 작업이 매우 높은 분해능을 가짐을 알 수 있었으며 또한 지반 침하 지역을 조사하고 이를 평가함에 있어 $2{\sim}3$차원 전기비저항탐사가 매우 유용함을 확인할 수 있었다. 이러한 탐사 결과를 바탕으로 연구지역 주변의 재해 취약정도를 작성하였다.

• 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.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2008년도 공동학술대회
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• pp.167-172
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• 2008

경북 문경군 가은읍 가은역 일대 석회암 분포 지역에서 지하 공동의 위치 및 발달 양상을 파악하기 위하여 고정밀 중력탐사를 하였다. 측점 간격은 4m로 하여 모두 약 1,100 측점에서 중력을 측정하였다. 잔여 부게 이상도에서 가장 낮은 중력 이상대를 지나는 3개의 측선에 대하여 MS(minimum support) 역산으로 밀도 분포 단면을 작성하였다. 또한, growing body 역산을 이용하여 3차원 밀도 분포 영상을 구하였다. 2차원과 3차원 밀도 분포도는 공동이 발달한 지역을 잘 가리키고 있으며, 석회암이 지하수에 부분적으로 용해되어 복잡한 형태의 공동 시스템을 구성하고 있고 부분적으로는 상당히 얕은 곳까지 발달해 있을 것으로 해석된다.

• 한국생산제조학회지
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• 제24권6호
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• pp.682-686
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• 2015

The objective of this study is to validate the performance of the current $k-{\epsilon}$ turbulence model for a single-phase turbulent natural convection, which has been considered an important phenomenon in nuclear safety. As a result, the natural convection problems in the 2D and 3D cavities previously studied are calculated by using the ANSYS Fluent software. The present results show that the current $k-{\epsilon}$ turbulent model accounting for the buoyancy effect is in good agreement with the previous results for the natural convection problems in the 2D and 3D cavities although some improvements should be required to get better prediction.