• 한국추진공학회지
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• 제17권1호
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• pp.61-69
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• 2013

핀틀 움직임에 의해 발생되는 큰 유동박리에 대해 적합한 2-방정식 난류모델의 압축성계수 보정모델을 판단하기 위하여 수치적 연구를 수행하였다. 난류모델은 저 레이놀즈수 k-${\varepsilon}$ 모델과 k-${\omega}$ SST 모델에 압축성 보정 모델(Wilcox와 Sarkar 모델)을 적용하여, 핀틀 노즐의 세부유동장을 관찰하고 노즐 벽면에서의 압력을 실험데이터와 비교 분석하였다. 마하디스크(Mach disk)의 위치와 박리영역에서의 압력 회복 형태는 난류모델에 따라 다르게 나타났으며, 각 난류모델에 압축성 보정을 적용하여 유동 박리 포획의 정확도를 개선하였다. 압축성이 보정된 k-${\varepsilon}$ 모델이 실험결과와 매우 잘 일치하였다.

• Journal of Pharmaceutical Investigation
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• 제40권4호
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• pp.237-244
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• 2010

This study investigated basic material properties and compressibility of commonly used pharmaceutical excipients. Five classes of excipients are selected including starch, lactose, calcium phosphate, microcrystalline cellulose (MCC), and povidone. The compressibility was evaluated using compression parameters derived from Heckel and Kawakita equation. The Heckel plot for lactose and dicalcium phosphate showed almost linear relationship. However, for MCC and povidone, curves in the initial phase of compression were observed followed by linear regions. The initial curve was considered as particle rearrangement and fragmentation and then plastic deformation at the later stages of the compression cycle. The Kawakita equation showed MCC exhibited higher compressibility, followed by povidone, lactose, and calcium phosphate. MCC undergoes significant plastic deformation during compression bringing an extremely large surface area into close contact and facilitating hydrogen bond formation between the plastically deformed, adjacent cellulose particles. Lactose compacts are consolidated by both plastic deformation and fragmentation, but to a larger extent by fragmentation. Calcium phosphate has poor binding properties because of its brittle nature. When formulating tablets, selection of suitable pharmaceutical excipients is very important and they need to have good compression properties with decent powder flowability. Material properties tested in this study might give a good guide how to select excipients for tablet formulations and help the formulation scientists design the optimum ones.

• 항공우주시스템공학회지
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• 제12권5호
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• pp.40-47
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• 2018

초음속 수축-확대 사각 노즐 내 강한 유동 박리를 동반한 초음속 유동에 적합한 난류 모델과 압축성 보정 모델을 평가하였다. 난류 모델로는 Yang과 Shih의 Low-Re $k-{\varepsilon}$ 모델, Menter의 $k-{\omega}$ SST모델, Wilcox의 $k-{\omega}$ 모델을 평가하였다. 압축성 효과를 보다 정확하게 예측하기 위하여 각각의 난류 모델에 Sarkar와 Wilcox의 압축성 보정 모델을 적용하였다. 각 난류 모델과 압축성 보정 모델의 결과는 실험 데이터와 비교하여 분석을 하였다. 난류 모델에 따라 충격파의 위치와 압력 회복률이 다르게 나타났으나 압축성 보정을 통해 더욱 개선된 결과를 얻었다.

• 한국지반공학회논문집
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• 제22권12호
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• pp.57-65
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• 2006

낙동강 하구지역에는 부산점토라고 불리는 연약점토가 두텁게 분포하고 있다. 과거 10년 동안에 대단위 지반개량 사업이 수행되어 왔지만, 주로 시료교란 때문에 압밀침하량과 시간을 아주 과소평가하여 왔었다. 이를 극복하기 위하여 부산점토에 대한 체계적인 지반조사에 의하여 압축특성을 규명할 필요가 요구되었다. 따라서 본 연구에서는 해안지역의 두 현장에서 개선된 시료채취기술을 적용하여 얻어진 시료에 대하여 지질조사, 불교란 및 교란 시료에 대한 압밀실험이 수행되었다. 이 결과를 이용하여 각종 압축정수의 산정과 그들의 상관성을 규명하였으며, 특히 퇴적환경에 따라 물리적 특성, 구조수준, 교란도 및 압축정수의 변화를 분석하였다.

• 한국수소및신에너지학회논문집
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• 제34권2호
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• pp.162-168
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• 2023

The fast refueling process of compressed hydrogen has an important impact on the filling efficiency and safety. With the development and use of hydrogen energy, the demand for precision measurement of filling hydrogen thermodynamic parameters is also increasing. In this paper, the compressibility factor calculation model of high-pressure hydrogen gas was studied, and the basic equation of state and thermo-physical parameters were calculated. The hydrogen density data provided by the National Institute of Standards and Technology was compared with the calculation results of each model. Results show that at a pressure of 0.1-100 MPa and a temperature of 233-363 K, the calculation accuracy of the Zheng-Li equation of state was less than 0.5%. In the range of 0.1-70 MPa, the accuracy of Redich-Kwong equation is less than 3%. The hydrogen pressure more influences on the compressibility factor than the hydrogen temperature does. Using the Zheng-Li equation of state to calculate the compressibility factor of on-board high pressure hydrogen can obtain high accuracy.

• Journal of applied mathematics & informatics
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• 제25권1_2호
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• pp.51-66
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• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.105-106
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• 2002

An expanded scheme of direct numerical solution method for solving the Reynolds' equation in the boundary fitted coordinate systems for the gas lubrication with ultra low clearance is presented. Skewed slider is calculated by this scheme and results are compared to the original direct numerical solution. The modified scheme has advantages in stability in high compressibility number region. At the lower A region the difference in results of original and modified method is several percents.

• 대한조선학회논문집
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• 제32권1호
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• pp.141-146
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• 1995

본 연구에서는 2축 방향의 압축/인장 하중을 받는 단순지지된 평판에 대하여 소성 압축성을 고려한 소성좌굴해석을 수행하였다. 2축하중을 받는 직사각형 평판의 소성 좌굴은 두개의 기계역학적 개념에 의해 지배를 받는데, 인장 강화와 소성 열화가 그것으로 인장과 압축이 적절히 결합함으로써 좌굴강도를 결정할 수 있게 된다. 소성 압축성을 고려하기 위해, Drucker-Prayer의 소성 포텐셜이론을 택하였다. 소성 변형률이 작을 때와 재질의 등방성 경화만을 가정하면 직사각형 평판에 관한 일반적인 고유방정식을 유도할 수 있게 된다.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.614-617
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulations of three dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence free flow field at each physical time step. The one equation Spalart-Allmaras turbulence model has been adopted to solve the high-Reynolds number flow fields. This method has been applied to calculate the steady flow fields around submarine configurations and unsteady flow fields around a 3-D infinite cylinder.