• Geomechanics and Engineering
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• 제15권6호
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• pp.1135-1141
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• 2018

Volume changes of soils induced by inorganic acids cause severe foundation and superstructure failures in industrial buildings. This study aimed to assess the potential of fly ash to control volume changes in soils under acidic environment. Two soils such as black cotton soil predominant with montmorillonite and kaolin clay predominant with kaolinite were used for the present investigation. Both soils exhibited an increase in swelling subjected to phosphoric acid contamination. Ion exchange reactions and mineralogical transformations lead to an increase in swelling and a decrease in compressibility in black cotton soil, whereas phosphate adsorption and mineral dissolution lead to an increase in swelling and compressibility in case of kaolin clay. Different percentages of Class F fly ash obtained from Ramagundam national thermal power station were used for soil treatment. Fly ash treatment leads to significant reduction in swelling and compressibility, which is attributed to the formation of aluminum phosphate cements in the presence of phosphoric acid.

• 대한조선학회논문집
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• 제48권6호
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• pp.581-591
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• 2011

This paper describes the air compressibility effect in the CFD simulation of water impact load prediction. In order to consider the air compressibility effect, two sets of governing equations are employed, namely the incompressible Navier-stokes equations and compressible Navier-Stokes equations that describe general compressible gas flow. In order to describe violent motion of free surface, volume-of-fluid method is utilized. The role of air compressibility is presented by the comparative study of water impact load obtained from two different air models, i.e. the compressible and incompressible air. For both cases, water is considered as incompressible media. Compressible air model shows oscillatory behavior of pressure on the solid surface that may attribute to the air-cushion effect. Incompressible air model showed no such oscillatory behavior in the pressure history. This study also showed that the CFD simulation can capture the formation of air pockets enclosed by water and solid surface, which may be the location where the air compressibility effect is dominant.

• 대한기계학회논문집A
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• 제21권5호
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• pp.735-745
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• 1997

In this study, the compressibility of resin was considered in filling analysis to account for the possible packing type flow. A numerical simulation program employing a hybrid finite element/finite difference scheme was developed to solve Hele-Shaw flow of the compressible viscous fluid at non-isothermal conditions. To advance the melt front, a control volume approach was adopted. Thin complex 3-D shapes of cavities, runners, and sprues were discretized by employing triangular, cylindrical and/or rectangular strip elements. Mass conservation was applied to each control volume to solve for the pressure distribution. Directly applying a constant mass flow rate at the inlet removes calculation of the apparent pressure boundary conditions, resulting in better simulation condition. The Cross model was used to model viscosity and the Tait equation was employed to represent density as a function of temperature and pressure. The validity of the developed program was verified through comparisons with available data in the literature and the effect of compressibility on the pressure distribution was discussed. To reduce computation time, 1-D and 2-D elements were used instead of applying triangular elements and the numerical results were compared to each other.

• 자원환경지질
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• 제47권3호
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• pp.247-254
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• 2014

불균질한 자연균열 저류층에서 암체의 압축률은 매우 작은 값을 가지는 반면에 균열의 압축률은 상대적으로 큰 값을 갖는다. 균열의 압축률을 포함한 유효 압축률을 고려하지 않을 경우에는 균열의 간극 변화로 인한 공극 부피의 변화를 반영할 수 없기 때문에 정확한 오일 회수를 예측할 수 없다. 본 연구에서는 기존의 연구들에서 암체의 압축률만을 고려하여 오일 회수를 분석했던 것과 달리, 암체와 균열의 압축률을 모두 고려한 유효 압축률을 적용해서 오일 회수량을 분석하였다. 폴리머 공법에서 균열의 압축률이 폴리머의 주입에 미치는 영향을 이해하기 위해, 폴리머의 분자량, 농도, 주입속도에 따른 오일 회수량을 분석하였다. 유효 압축률을 고려할 경우 폴리머 분자량, 농도, 주입속도가 높아질수록 유효 압축률을 고려하지 않은 경우가 고려한 경우보다 누적 오일 생산량이 높게 나타났다. 또한 공저 압력의 경우에도 유효 압축률을 고려하지 않은 경우가 고려한 경우보다 빠르게 급감하여 오일 생산량에 영향을 주는 것을 확인할 수 있다.

• 대한토목학회논문집
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• 제28권1C호
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• pp.9-17
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• 2008

본 연구에서는 압밀 중에 위치별 간극수압의 측정을 통하여 시료 내 여러 위치에서 투수계수를 산정할 수 있는 이론해를 제시하였으며, 이를 바탕으로 간극비 및 체적압축계수를 산정할 수 있는 방법을 제안하였다. 또한 여러 위치에서 간극수압을 측정할 수 있는 방사내측배수가 가능한 대형압밀시험기를 제작하고 카올리나이트를 이용하여 압밀시험을 실시하였다. 시험결과로부터 압밀 중 투수계수, 간극비, 체적압축계수의 변화 및 시료 내 위치별 분포를 평가하였으며, 압밀완료 후 시료의 함수비 측정으로 평가된 값들과의 비교를 통하여 실험결과의 신뢰성을 검증하였다. 실험결과 투수계수, 체적압축계수, 간극비는 압밀 중 감소하며, 재하단계에 따라서도 감소함을 확인하였다. 또한 그 분포형태는 배수면 근처에서 가장 작고 배수거리에 따라 증가하며 비배수 경계면 근처에서는 오히려 약간 작은 것으로 나타났다.

• International Journal of Aeronautical and Space Sciences
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• 제12권4호
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• pp.318-330
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• 2011

This paper investigates the convergence characteristics of the modified artificial compressibility method proposed by Turkel. In particular, a focus is mode on the convergence characteristics due to variation of the preconditioning factor (${\alpha}_u$) and the artificial compressibility (${\beta}$) in conjunction with an upwind method. For the investigations, a code using the modified artificial compressibility is developed. The code solves the axisymmetric incompressible Reynolds averaged Navier-Stokes equations. The cell-centered finite volume method is used in conjunction with Roe's approximate Riemann solver for the inviscid flux, and the central difference discretization is used for the viscous flux. Time marching is accomplished by the approximated factorization-alternate direction implicit method. In addition, Menter's k-${\omega}$ shear stress transport turbulence model is adopted for analysis of turbulent flows. Inviscid, laminar, and turbulent flows are solved to investigate the accuracy of solutions and convergence behavior in the modified artificial compressibility method. The possible reason for loss of robustness of the modified artificial compressibility method with ${\alpha}_u$ >1.0 is given.

• Geomechanics and Engineering
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• 제1권1호
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• pp.1-15
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• 2009

Many aspects of the behavior of sands are affected by the content of non-plastic fine particles and these various aspects should be included in a constitutive model for the soil behavior. The fines content affects maximum and minimum void ratios, compressibility, shear strength, and static liquefaction under undrained conditions. Twenty-eight undrained triaxial compression tests were performed on mixtures of sand and fine particles with fines contents of 0, 10, 20, 30, 50, 75, and 100% to study the effects of fines on void ratio, compressibility, and the occurrence of static liquefaction. The experiments were performed at low consolidation pressures at which liquefaction may occur in near-surface, natural deposits. The presence of fines creates a particle structure in the soil that is highly compressible, enhancing the potential for liquefaction, and the fines also alter the basic stress-strain and volume change behavior, which should be modeled to predict the occurrence of static liquefaction in the field. The void ratio at which liquefaction occurs for each sand/fines mixture was determined, and the variation of compressibility with void ratio was determined for each mixture. This allowed a relation to be determined between fines content, void ratio, compressibility, and the occurrence of static liquefaction. Such relations may vary from sand to sand, but the present results are believed to indicate the trend in such relations.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.387-397
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• 2013

An assessment of two-equation turbulence models, the low Reynolds k-${\varepsilon}$ and k-${\omega}$ SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.49-54
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• 2007

오일러나 Navier-Stokes방정식을 통한 터빈 캐스케이드 유동 해석은 비교적 정확한 해를 구할 수 있으나 많은 계산 시간을 필요로 한다. 비점성, 비압축성 유동에 적용이 가능한 패널법은 빠르고 합리적인 유동 정보를 얻을수 있지만 고속 유동의 경우 압축성 보정이 반드시 이뤄져야한다. 본 논문에서는 압축성이 보정된 패널법을 이용하여 터빈 블레이드 표면의 속도 분포를 계산하였다. 그 결과, 압축성이 보정된 패널법의 결과는 실험이나 유한 체적법에 의해 계산된 결과와 잘 일치하였다.

• 한국추진공학회지
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• 제12권1호
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• pp.23-28
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• 2008

오일러나 Navier-Stokes 방정식을 통한 터빈 캐스케이드 유동 해석은 비교적 정확한 해를 구할 수 있으나 많은 계산 시간을 필요로 한다. 비점성, 비압축성 유동에 적용이 가능한 패널법은 빠르고 합리적인 유동 정보를 얻을 수 있지만 고속 유동의 경우 압축성 보정이 반드시 이뤄져야한다. 본 논문에서는 압축성이 보정된 패널법을 이용하여 터빈 블레이드 표면의 속도 분포를 계산하였다. 그 결과, 압축성이 보정된 패널법의 결과는 유한 체적법에 의해 계산된 결과와 잘 일치하였다.