• Korea-Australia Rheology Journal
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• 제19권2호
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• pp.67-73
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• 2007

A finite volume method (FVM) base on the SIMPLE algorithm as the pressure correction strategy and the traditional staggered mesh is used to investigate steady, fully developed flow of Oldroyd-3-constant fluids through a duct with square cross-section. Both effects of the two viscoelastic material parameters, We and ${\mu}$, on pattern and strength of the secondary flow are investigated. An amusing sixteen vortices pattern of the secondary flow, which has never been reported, is shown in the present work. The reason for the changes of the pattern and strength of the secondary flow is discussed carefully. We found that it is variation of second normal stress difference that causes the changes of the pattern and strength of the secondary flow.

• Journal of Advanced Marine Engineering and Technology
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• 제25권5호
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• pp.1037-1049
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• 2001

Considerable interest has evolved in the flow of non-Newtonian fluids in channels of noncircular cross section in compact heat exchanges. Analytical solution was developed for prediction of the flow rate and maximum velocity in steady laminar flow of any incompressible, time-independent non-Newtonian fluids in straight closed and open channels of arbitrary, but axially unchanging cross section. The geometric parameters and function of shear describing the behavior of the fluid model were evaluated for fluid flow among a bundle of rods arranged in triangular and square array. Numerical values of dimensionless maximum velocities, mean velocities, pressure-drop-flow parameters and friction factors were evaluated as a function of porosity and pitch-to-radius ratio.

• 대한기계학회논문집B
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• 제23권1호
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• pp.149-157
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• 1999

Heat transfer in a duct is augmented remarkably by rib turbulators. However, increasing friction loss is accompanied due to ribs disturbing flows. Hence, pressure drops and heat transfer are considered simultaneously to decide heat/mass transfer performance in a rib-roughened duct. In the present study, the effects of rib cross section shape on pressure drop through a duct are investigated as well as those on heat transfer characteristics. The results show that the characteristics of heat/mass transfer and friction loss in the duct roughened with triangular ribs are similar to those with square ribs, while significantly different from those with semicircular ribs. The best performance in the duct is obtained by using semicircular shaped ribs among three types of ribs for the large rib angles of ${\alpha}{\geq}63^{\circ}$.

• 한국정밀공학회지
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• 제19권4호
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• pp.109-116
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• 2002

The solution of the aircraft wing spar cross-section area optimization problem is obtained by the response surface method. The object function of the problem is wing total weight, design variables are spar cross-section areas, constraints are the conditions that the stresses at the each spar is less than the allowable stress. D-Optimal condition is utilized to obtain the experimental points to construct the response surfaces. D-Optimal experimental points are obtained by the commercial software "Deign-Expert". Response values for the object function and constraints for each experimental point are calculated by the NASTRAN. Response surfaces for object function and constraints are approximated from the response values by the least square method. The optimization solution is obtained by the DOT for the response surfaces of object function and constraints. The optimization results obtained from the response surface are compared with the results obtained by the NASTRAN SOL200.

• Journal of Preventive Medicine and Public Health
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• 제24권1호
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• pp.29-36
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• 1991

A multiple regression analysis using ordinary least square (OLS) is frequently used for the projection of health expenditure as well as for the identification of factors affecting health care costs. Data for the analysis often have mixed characteristics of time series and cross section. Parameters as a result of OLS estimation, in this case, are no longer the best linear unbiased estimators (BLUE) because the data do not satisfy basic assumptions of regression analysis. The study theoretically examined statistical problems induced when OLS estimation was applied with the time series cross section data. Then both the OLS regression and time series cross section regression (TSCS regression) were applied to the same empirical da. Finally, the difference in parameters between the two estimations were explained through residual analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.917-918
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• 2012

• 대한토목학회논문집
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• 제29권1A호
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• pp.53-60
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• 2009

이 논문은 양단회전 후좌굴 변단면 기둥의 기하 비선형 해석에 관한 연구이다. 기둥의 변단면은 변화폭, 변화깊이, 정방형 변단면으로 채택하였다. Bernoulli-Euler 보 이론을 이용하여 후좌굴 기둥의 정확탄성곡선을 지배하는 미분방정식을 유도하였다. 이 미분방정식은 두 개의 미지수를 가지며 이러한 미분방정식을 풀 수 있는 수치해석 방법을 개발하였다. 후좌굴 기둥의 수치해석 결과로 평형경로, 정확탄성곡선 및 합응력을 산정하였다. 실험을 통하여 후좌굴 거동의 이론을 검증하였다.

• 대한기계학회논문집B
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• 제33권2호
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• pp.124-132
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• 2009

Experiments have been performed to investigate fluid-elastic instability of tube bundles, subjected to twophase cross flow. Fluid-elastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and the threshold flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

• 설비공학논문집
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• 제14권12호
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• pp.1004-1013
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• 2002

Turbulent carbon dioxide flows and cooling heat transfers under supercritical state in a straight duct with a square cross-section are numerically analyzed employing low Reynolds number $\kappa-\varepsilon$ model and algebraic stress model. The flow is assumed to be (quasi-incompressible. Predicted Nusselt number and friction factor are compared with the experimental data, Blasius correlation for friction factor and Dittus-Boelter correlation for Nusselt number. Computational results for the Fanning's friction factor agree well with the all Rohsenow and Choi's correlation, Liou and Hwang's experimental data and Blasius correlation. The results obtained by algebraic stress model agree more with the Liou and Hwang's experimental data, while the results obtained by low Reynolds number $\kappa-\varepsilon$ model agree more with Blasius correlation. In the computation of Nusselt number, Dittus-Boelter correlation can not exactly fit the computational results. Therefore we propose the new correlation$Nu=0.053Re^{0.73}Pr^{0.4}$for the turbulent cooling heat transfer of carbon dioxide under supercritical state.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.550-555
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• 2003

When a shock wave arrives at an open end of tube, an impulse wave is discharged from the tube exit and complicated flow is formed near tube exit. The flow field is influenced by the cross-sectional geometry of tube exit, such as circular, square, rectangular, trapezoid and etc. In the current study, three-dimensional propagation characteristics of impulse wave discharged from the tube exit with non-circular cross section are numerically investigated using a CFD method. Total variation diminishing (TVD) scheme is used to solve the three-dimensional, unsteady, compressible Euler equations. Computations are performed for the Mach numbers of the incident shock wave $M_{s}$ below 1.5. The results obtained show that the peak pressure of the impulse wave and propagation directivity depends on the cross-sectional geometry of tube exit and the Mach number of incident shock wave.