• 대한기계학회논문집B
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• 제38권7호
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• pp.625-638
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• 2014

본 연구에서는 천연가스 유량 측정에 사용되는 임계유동함수(CFF)를 AGA8-dc 상태방정식으로 계산할 때 CFF 계산값의 불확도를 평가하였다. CFF 계산에 사용되는 엔탈피, 엔트로피, 음속 식은 불확도 분석이 가능하도록 무차원 헬름홀츠 자유에너지(Helmholtz free energy, HFE)와 이의 편도함수로 표현하였고, HFE의 불확도를 추정하였다. 압축인자의 불확도에 의해 유발되는 종속 변수의 불확도를 반영하기 위해 AGA8-dc 압축인자 식을 해당 불확도만큼 편차가 생기는 형태로 변형하였고, 각 불확도 요인별로 불확도 기여도 평가 모델을 만들었으며, 이를 CFF 계산 프로그램에 적용하였다. 그 결과 CFF의 불확도는 압력 10, 50, 100 bar 에서 각각 0.025, 0.055, 0.112 % 정도로 평가 되었고 압력에 비례하여 증가하는 것을 확인하였다. 또한 본 결과를 기존 CFF 국제비교시험결과(1999년)에 적용한 결과 각 기관별 CFF 값의 차이를 적절히 설명하는 것도 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.545-550
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• 2001

A two-dimensional laminar flow through a channel, on which a couple of symmetric vertical fins are attached, is investigated. The stokes flow for this channel flow is investigated analytically and laminar flow numerically. For analytic solution, the method of eigen function expansion and collocation method are employed. For numerical solution, finite difference method(FDM) is used to obtain vorticity and stream function. From the results, streamline patterns are shown and the pressure drop due to the attached fins is calculated, which depends on the length of fins and Reynolds number. While $Re, streamline pattern is symmetric, a pair of additional asymmetric solutions appear for $Re>Re_c$, where the critical Reynolds number $Re_c$ depends on the length of the fin.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.356-359
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• 2007

In this paper, the stability of a rotating cantilever pipe conveying fluid with a crack is investigated by the numerical method. That is, the influences of the rotating angular velocity, mass ratio and crack severity on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived using the Euler beam theory and the Lagrange's equation. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. Generally, the critical flow velocity for flutter is proportional to the angular velocity and the depth of crack. Also, the critical flow velocity and stability maps of the rotating pipe system as a function of mass ratio for the changing each parameter are obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.652-657
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• 2001

Computational work using the axisymmetric, compressible, Navier-Stokes Equations is carried out to predict the discharge coefficient of mass flow through a micro-critical nozzle. Several kinds of turbulence models and wall functions are employed to validate the computational predictions. The computed results are compared with the previous experimented ones. The present computations predict the experimental discharge coefficients with a reasonable accuracy. It is found that the standard $k-\varepsilon$ turbulence model with the standard wall function gives a best prediction of the discharge coefficients. The displacement thickness of the nozzle wall boundary layer is evaluated at the nozzle throat and is well compared to a prediction obtained by an empirical equation. The resulting displacement thickness of the wall boundary layer is about 2% to 0.6% of the diameter of the nozzle throat for the Reynolds numbers of 2000 to 20000.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.292-296
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• 2008

A new method of evaluating critical damage values of commercial materials is presented in this paper. The method is based on the previous study of the methodology [1] of acquisition of true stress-strain curves or flow stress curves over large strain from the tensile test in which the flow stress is described by the Hollomon law-like form, that is, by the strain dependent strength coefficient and the strain hardening exponent. The strain hardening exponent is calculated from the true strain at the necking point to meet the Considere condition. The strength coefficient is assumed to be constant before necking and represented by a piecewise linear function of strain after necking. With the predicted flow stress, a tensile test is simulated by a rigid-plastic finite element method with higher accuracy of less than 0.5% error between experiments and predictions. The instant when the fracture begins and thus the critical damage is obtained is determined by observing the stress variation at the necked region. It is assumed that the fracture due to damage begins when the pattern of stress around the necked region changes radically. The method is applied to evaluate the critical damage of a low carbon steel.

• Journal of Electrical Engineering and Technology
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• 제8권1호
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• pp.53-63
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• 2013

To guide the decision making of the expert engineer specialized in power system operation and control; the practical OPF solution should take in consideration the critical situation due to severe loading conditions and fault in power system. Differential Evolution (DE) is one of the best Evolutionary Algorithms (EA) to solve real valued optimization problems. This paper presents simple Differential Evolution (DE) Optimization algorithm to solving multi objective optimal power flow (OPF) in the power system with shunt FACTS devices considering voltage deviation, power losses, and power flow branch. The proposed approach is examined and tested on the standard IEEE-30Bus power system test with different objective functions at critical situations. In addition, the non smooth cost function due to the effect of valve point has been considered within the second practical network test (13 generating units). The simulation results are compared with those by the other recent techniques. From the different case studies, it is observed that the results demonstrate the potential of the proposed approach and show clearly its effectiveness to solve practical OPF under contingent operation states.

• IMMUNE NETWORK
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• 제5권2호
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• pp.105-109
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• 2005

Background: Dendritic cells (DCs) are the most potent APCs (antigen-presenting cells) and playa critical role in immune responses. Galectin-3 is a biological lectin with a beta-galactoside binding affinity. Recently, proteomic analysis revealed the presence of galectin-3 in the exosome of mature DCs. However, the expression and function of galectin-3 in DCs remains unclear yet. Methods: We used bone marrow-derived DCs of mouse and showed the expression of galectin-3 in DCs by using flow cytometry analysis and Western blot analysis. Results: Galectin-3 was determined as single band of 35 kDa in Western blot analysis. Flow cytometry analysis showed the major growth factor for DCs, granulocyte-macrophage colony stimulating factor (GM-CSF) and maturing agents, anti-CD40 monoclonal antibody (mAb) and lipopolysaccharide (LPS) consistently increased the intracellular expression of galectin-3 in DCs compared to medium alone. In addition, DCs treated with maturing agents did marginally express galectin-3 on their surface. Conclusion: This study suggests that galectin-3 in DCs may be regulated by critical factors for DC function.

• 설비공학논문집
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• 제17권12호
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• pp.1106-1112
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• 2005

An experimental investigation was performed to develop an empirical correlation of R-410A flowing through short tube orifices working near the critical region. Tests were executed by varying upstream pressure from 2,619 kPa to 4,551 kPa, and upstream subcooling from 2.8 and $11.1^{\circ}C$. The experimental data were represented as a function of major operating parameters and short tube diameter. As compared to mass flow trends at normal upstream pressures, flow dependency on upstream subcooling became more significant at high upstream pressures due to a higher density change. Based on the database obtained from this study and literature, an empirical correlation was developed from a power law form of dimensionless parameters generated by the Buckingham Pi theorem. The correlation yielded good agreement with the data. Approximately $92\%$ of the data were correlated within a relative deviation of $5\%$.

• Journal of applied mathematics & informatics
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• 제35권3_4호
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• pp.241-260
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• 2017

An analysis is made to study the solute transport in a Casson fluid flow through an annulus in presence of oscillatory flow field and determine how this flow influence the solute dispersion along the annular region. Axial dispersion coefficient and the mean concentration expressions are calculated using the generalized dispersion model. Dispersion coefficient in oscillatory flow is found to be a function of frequency parameter, Schmidt number, and the pressure fluctuation component besides its dependency on yield stress of the fluid, annular gap and time in the case of steady flow. Due to the oscillatory nature of the flow, the dispersion coefficient changes cyclically and the amplitude and magnitude of the dispersion increases initially with time and reaches a non - transient state after a certain critical time. This critical value varies with frequency parameter and independent of the other parameters. It is found that the presence of inner cylinder and increase in the size of the inner cylinder inhibits the dispersion process. This model may be used in understanding the dispersion phenomenon in cardiovascular flows and in particular in catheterized arteries.

• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1706-1710
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• 2005

In a case of computer simulation used for the verification of pneumatic system performance one of the main problems is that various parameters can be used to describe flow characteristics of the system components. The Standard ISO 6358 offers two parameters: the sonic conductance C and the critical static pressure ratio b, but the parameters can not be directly utilised in an analysis of a pneumatic system. In the standard analysis there is applied the airflow coefficient ${\mu}$, but it is not presented in the vendors' catalogues. In the paper the numerical algorithm for calculation of the airflow coefficient ${\mu}$. (which is required for computer simulation) as a function of sonic conductance C and a critical pressure ratio b (recommended by the standard) is presented. Additionally, because of the iterative character of the described algorithm, an artificial neural network approach to solve the problem is proposed.