• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.437-440
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• 2005

In the present work, characteristics of the flow in CAGE of a steam turbine LP/HP Bypass control valve for thermal power plant are investigated. The flow field is analyzed numerically by solving steady three-dimensional Reynolds-averaged Navier-Stokes equations. Shear stress transport (SST) model is used as turbulence closure.

• Journal of Chest Surgery
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• 제32권6호
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• pp.495-503
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• 1999

Background: We tested the technical feasibility of fetal cardiac bypass and collected baseline data on the fetal hemodynamics and placental functions related to the cardiopulmonary bypass in the fetal lamb model. Material and Method: Eleven fetuses at 120 to 150 days of gestation were subjected to bypass via trans-sternal approach with a 12 G pulmonary arterial cannula and 14 to 18 F venous cannula for 30 minutes. All ewes received general anesthesia with ketamine. In all the fetuses, no anesthetic agents were used except muscle relaxant. Eight served as a group in which placenta was excluded from the extracorporeal circulation by clamping the umbilical cord during the bypass(the oxygenator group) and in the remaining three, the placenta worked as the only source of oxygen supply(the placenta group). Observations were made every 10 minute during a 30-minute bypass and 30-minute post bypass period. No prostaglandin inhibitors were used both in ewes and in fetuses. Result: Weights of the fetuses ranged from 1.9 to 5.2 kg. In the oxygenator group, means of arterial pressure, PaO2, atrial pressure, heart rate, and bypass flow rate ranged 69.8 to 82.6 mmHg, 201.7 to 220.9 mmHg, 4.1 to 4.3 mmHg, 169 to 182/min, and 140.3 to 164.0 ml/kg/min, respectively during bypass, but rapid deterioration of the fetal cardiac functions and the placental gas exchange was observed after the cessation of bypass. In the placenta group, means of arterial pressure decreased from 44.7 to 14.4 mmHg and means of PaCO2 increased from 61.9 to 129.6 mmHg during bypass. Flow rate was suboptimal(74.3 to 97.0 ml/kg/min) during bypass. All hearts fibrillated immediately after the discontinuation of bypass. Conclusion: In this study, the technical feasibility of fetal cardiopulmonary bypass was confirmed in the fetal lamb model. However, further studies with modifications of the bypass including an addition of prostaglandin inhibitor, an application of the total spinal anesthesia on the fetus, a creation of more concise bypass circuit, and a use of active pump are mandatory to improve the outcome.

• Journal of Mechanical Science and Technology
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• 제19권3호
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• pp.905-912
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• 2005

A computational investigation of blood flow in a coronary artery grafted by artificial bypass was performed to determine such geometric parameters as the curvature of radius, approach length, and angle of end-to-side anastomosis. Transient flow features in the host artery were computed using FVM and SIMPLE algorithms. We compared flow distributions and wall shear stresses in two simple models, planar and non-planar, and confirmed that the non-planar bypass model was more conducive to suppressing intimal hyperplasia. Our non-planar model with $60^{\circ}$ of anastomosis and a 1.0 diameter approach length and radius of curvature predicts a relatively small, spatially-extended high-OSI (>0.01) zone, as well as an increased average wall shear stress on this zone.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제26권6호
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• pp.823-832
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• 2002

A modified $textsc{k}$-$\varepsilon$model is proposed for calculation of transitional boundary-layer flows with changing pressure gradient. In order to develop the model for this problem, the flow is divided into three regions; pre-transition region, transition region and fully turbulent region. The effect of pressure gradient is taken into account in stream-wise intermittency factor, which bridges the eddy-viscosity models in the pre-transition region and the fully turbulent region. From intermittency data in various flows, Narashima＇s intermittency function, F(${\gamma}$), has been found to be proportional to $\chi$$^{n}$ according to the extent of pressure gradient. Three empirical correlations of intermittency factor being analyzed, the best one was chosen to calculate three benchmark cases of bypass transition flows with different free-stream turbulence intensity under arbitrary pressure gradient. It was found that the variations of skin friction and shape factor as well as the profiles of mean velocity in the transition region were very satisfactorily predicted.

• Journal of the Korean Society of Propulsion Engineers
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• 제14권6호
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• pp.79-88
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• 2010

This paper dealt with the performance modeling of a low bypass turbofan engine for supersonic aircraft. The Pratt and Whitney F100-PW-229 engine has been employed for low bypass turbofan engine performance modeling. Generally, the complete commercially-classified informations concerning the engine are unknown. The components' generic characteristics and assumptions made in order to build the F100-PW-229 engine performance model using by the published data from the open literature as basic data are described. Through the comparison of engine performance model's analysis data using Gasturb11 with engine deck data showed that the engine performance model was evaluated to be properly constructed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.239-248
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• 2010

This paper dealt with the Performance Modeling of a low-bypass turbofan engine for supersonic aircraft. The Pratt and Whitney F100-PW-229 engine has been employed for low-bypass turbofan engine performance modeling. Generally, The complete commercially-classified information concerning the engine are unknown. So, Components' generic characteristics are described and assumptions made in order to model the F100-PW-229 engine performance model. All the analysis has been undertaken using published data taken from the open literature. The results of the Engine Performance using Gasturb11 showed that the Engine performance model was evaluated to be properly constructed.

• Journal of Chest Surgery
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• 제44권2호
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• pp.89-98
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• 2011

Background: Although considerable efforts have been made to improve the graft patency in coronary artery bypass surgery, the role of biomechanical factors remains underrecognized. The aim of this study is to investigate the influences of geometric configurations of the bypass graft on hemodynamic characteristics in relation to anastomosis. Materials and Methods: The Numerical analysis focuses on understanding the flow patterns for different values of inlet and distal diameters and graft angles. The Blood flow field is treated as a two-dimensional incompressible laminar flow. A finite volume method is adopted for discretization of the governing equations. The Carreau model is employed as a constitutive equation for blood. In an attempt to obtain the optimal aorto-coronary bypass conditions, the blood flow characteristics are analyzed using in vitro models of the end-to-side anastomotic angles of $45^{\circ}$, $60^{\circ}$ and $90^{\circ}$. To find the optimal graft configurations, the mass flow rates at the outlets of the four models are compared quantitatively. Results: This study finds that Model 3, whose bypass diameter is the same as the inlet diameter of the stenosed coronary artery, delivers the largest amount of blood and the least pressure drop along the arteries. Conclusion: Biomechanical factors are speculated to contribute to the graft patency in coronary artery bypass grafting.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제27권1호
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• pp.65-71
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• 2017

This work presents a comparative work on the ride comfort of a quarter car suspension system between two different magneto-rheological (MR) dampers; one is conventional type without bypass hole and the other is featured by several bypass holes in the piston. As a first step, two different MR dampers are designed on the basis of the governing equation and manufactured with same geometric dimensions except the bypass holes. After investigating the field-dependent damping properties, two dampers are installed to the quarter car suspension system. The suspension model is then derived and a sky-hook controller is implemented to identify vibration control performance under random road. It is shown that the suspension system with MR damper featured by the bypass holes can provide much better ride quality than the case without the bypass holes. This is validated via experimental implementation.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.998-999
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• 2014

This paper proposes a method for damping force modeling of magnetorheological (MR) damper featuring bypass hole. After describing configuration and of the MR damper, a damping force modeling of the MR damper is derived based on Bingham model of MR fluid. MR damper consists of piston, accumulator, gap, bypass hole and coil. Damping force is consists of spring force induced by accumulator, viscous force induced at gap and bypass hole, and controllable force induced at gap.